diff --git a/src/tint/inspector/inspector_test.cc b/src/tint/inspector/inspector_test.cc
index 5a190f6..b892302 100644
--- a/src/tint/inspector/inspector_test.cc
+++ b/src/tint/inspector/inspector_test.cc
@@ -1811,7 +1811,7 @@
         "foo_type",
         utils::Vector{
             Member("0i32", ty.i32()),
-            Member("b", ty.array(ty.u32(), 4_u, /*stride*/ 16), utils::Vector{MemberAlign(16_u)}),
+            Member("b", ty.array(ty.u32(), 4_u, /*stride*/ 16), utils::Vector{MemberAlign(16_i)}),
         });
 
     AddUniformBuffer("foo_ub", ty.Of(foo_struct_type), 0, 0);
@@ -3239,7 +3239,7 @@
     // here the struct is expected to occupy 1024 bytes of workgroup storage.
     const auto* wg_struct_type = MakeStructTypeFromMembers(
         "WgStruct", utils::Vector{
-                        MakeStructMember(0, ty.f32(), utils::Vector{MemberAlign(1024_u)}),
+                        MakeStructMember(0, ty.f32(), utils::Vector{MemberAlign(1024_i)}),
                     });
 
     AddWorkgroupStorage("wg_struct_var", ty.Of(wg_struct_type));
diff --git a/src/tint/reader/wgsl/parser_impl.cc b/src/tint/reader/wgsl/parser_impl.cc
index 2c72d6a..cb7cb6a 100644
--- a/src/tint/reader/wgsl/parser_impl.cc
+++ b/src/tint/reader/wgsl/parser_impl.cc
@@ -3435,15 +3435,16 @@
     if (t == "align") {
         const char* use = "align attribute";
         return expect_paren_block(use, [&]() -> Result {
-            auto val = expect_positive_sint(use);
-            if (val.errored) {
+            auto expr = expression();
+            if (expr.errored) {
                 return Failure::kErrored;
             }
+            if (!expr.matched) {
+                return add_error(peek(), "expected align expression");
+            }
             match(Token::Type::kComma);
 
-            return create<ast::StructMemberAlignAttribute>(
-                t.source(), create<ast::IntLiteralExpression>(
-                                val.value, ast::IntLiteralExpression::Suffix::kNone));
+            return create<ast::StructMemberAlignAttribute>(t.source(), expr.value);
         });
     }
 
diff --git a/src/tint/reader/wgsl/parser_impl_error_msg_test.cc b/src/tint/reader/wgsl/parser_impl_error_msg_test.cc
index ac2161c..9fad55c 100644
--- a/src/tint/reader/wgsl/parser_impl_error_msg_test.cc
+++ b/src/tint/reader/wgsl/parser_impl_error_msg_test.cc
@@ -851,17 +851,9 @@
 }
 
 TEST_F(ParserImplErrorTest, GlobalDeclStructMemberAlignInvaldValue) {
-    EXPECT("struct S { @align(x) i : i32, };",
-           R"(test.wgsl:1:19 error: expected signed integer literal for align attribute
-struct S { @align(x) i : i32, };
-                  ^
-)");
-}
-
-TEST_F(ParserImplErrorTest, GlobalDeclStructMemberAlignNegativeValue) {
-    EXPECT("struct S { @align(-2) i : i32, };",
-           R"(test.wgsl:1:19 error: align attribute must be positive
-struct S { @align(-2) i : i32, };
+    EXPECT("struct S { @align(fn) i : i32, };",
+           R"(test.wgsl:1:19 error: expected align expression
+struct S { @align(fn) i : i32, };
                   ^^
 )");
 }
diff --git a/src/tint/reader/wgsl/parser_impl_struct_body_decl_test.cc b/src/tint/reader/wgsl/parser_impl_struct_body_decl_test.cc
index 3499b5c..ce56a67 100644
--- a/src/tint/reader/wgsl/parser_impl_struct_body_decl_test.cc
+++ b/src/tint/reader/wgsl/parser_impl_struct_body_decl_test.cc
@@ -60,12 +60,12 @@
 TEST_F(ParserImplTest, StructBodyDecl_InvalidAlign) {
     auto p = parser(R"(
 {
-  @align(nan) a : i32,
+  @align(if) a : i32,
 })");
     auto m = p->expect_struct_body_decl();
     ASSERT_TRUE(p->has_error());
     ASSERT_TRUE(m.errored);
-    EXPECT_EQ(p->error(), "3:10: expected signed integer literal for align attribute");
+    EXPECT_EQ(p->error(), "3:10: expected align expression");
 }
 
 TEST_F(ParserImplTest, StructBodyDecl_InvalidSize) {
diff --git a/src/tint/reader/wgsl/parser_impl_struct_member_attribute_test.cc b/src/tint/reader/wgsl/parser_impl_struct_member_attribute_test.cc
index 9bafaf0..f6957e4 100644
--- a/src/tint/reader/wgsl/parser_impl_struct_member_attribute_test.cc
+++ b/src/tint/reader/wgsl/parser_impl_struct_member_attribute_test.cc
@@ -110,13 +110,39 @@
               ast::IntLiteralExpression::Suffix::kNone);
 }
 
+TEST_F(ParserImplTest, Attribute_Align_Expression) {
+    auto p = parser("align(4 + 5)");
+    auto attr = p->attribute();
+    EXPECT_TRUE(attr.matched);
+    EXPECT_FALSE(attr.errored);
+    ASSERT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(attr.value, nullptr);
+
+    auto* member_attr = attr.value->As<ast::Attribute>();
+    ASSERT_NE(member_attr, nullptr);
+    ASSERT_TRUE(member_attr->Is<ast::StructMemberAlignAttribute>());
+
+    auto* o = member_attr->As<ast::StructMemberAlignAttribute>();
+    ASSERT_TRUE(o->expr->Is<ast::BinaryExpression>());
+    auto* expr = o->expr->As<ast::BinaryExpression>();
+
+    EXPECT_EQ(ast::BinaryOp::kAdd, expr->op);
+    auto* v = expr->lhs->As<ast::IntLiteralExpression>();
+    ASSERT_NE(nullptr, v);
+    EXPECT_EQ(v->value, 4u);
+
+    v = expr->rhs->As<ast::IntLiteralExpression>();
+    ASSERT_NE(nullptr, v);
+    EXPECT_EQ(v->value, 5u);
+}
+
 TEST_F(ParserImplTest, Attribute_Align_TrailingComma) {
     auto p = parser("align(4,)");
     auto attr = p->attribute();
     EXPECT_TRUE(attr.matched);
     EXPECT_FALSE(attr.errored);
     ASSERT_NE(attr.value, nullptr);
-    ASSERT_FALSE(p->has_error());
+    ASSERT_FALSE(p->has_error()) << p->error();
 
     auto* member_attr = attr.value->As<ast::Attribute>();
     ASSERT_NE(member_attr, nullptr);
@@ -157,17 +183,18 @@
     EXPECT_TRUE(attr.errored);
     EXPECT_EQ(attr.value, nullptr);
     EXPECT_TRUE(p->has_error());
-    EXPECT_EQ(p->error(), "1:7: expected signed integer literal for align attribute");
+    EXPECT_EQ(p->error(), "1:7: expected align expression");
 }
 
-TEST_F(ParserImplTest, Attribute_Align_MissingInvalid) {
-    auto p = parser("align(nan)");
+TEST_F(ParserImplTest, Attribute_Align_ExpressionInvalid) {
+    auto p = parser("align(4 + 5 << 6)");
     auto attr = p->attribute();
     EXPECT_FALSE(attr.matched);
     EXPECT_TRUE(attr.errored);
     EXPECT_EQ(attr.value, nullptr);
     EXPECT_TRUE(p->has_error());
-    EXPECT_EQ(p->error(), "1:7: expected signed integer literal for align attribute");
+
+    EXPECT_EQ(p->error(), "1:13: expected ')' for align attribute");
 }
 
 }  // namespace
diff --git a/src/tint/resolver/attribute_validation_test.cc b/src/tint/resolver/attribute_validation_test.cc
index e648562..8d20673 100644
--- a/src/tint/resolver/attribute_validation_test.cc
+++ b/src/tint/resolver/attribute_validation_test.cc
@@ -89,7 +89,7 @@
                                                                 AttributeKind kind) {
     switch (kind) {
         case AttributeKind::kAlign:
-            return {builder.MemberAlign(source, 4_u)};
+            return {builder.MemberAlign(source, 4_i)};
         case AttributeKind::kBinding:
             return {builder.Binding(source, 1_a)};
         case AttributeKind::kBuiltin:
@@ -627,8 +627,8 @@
     Structure("mystruct", utils::Vector{
                               Member("a", ty.i32(),
                                      utils::Vector{
-                                         MemberAlign(Source{{12, 34}}, 4_u),
-                                         MemberAlign(Source{{56, 78}}, 8_u),
+                                         MemberAlign(Source{{12, 34}}, 4_i),
+                                         MemberAlign(Source{{56, 78}}, 8_i),
                                      }),
                           });
     EXPECT_FALSE(r()->Resolve());
@@ -659,6 +659,89 @@
               "position builtin");
 }
 
+TEST_F(StructMemberAttributeTest, Align_Attribute_Const) {
+    GlobalConst("val", ty.i32(), Expr(1_i));
+
+    Structure("mystruct", utils::Vector{Member("a", ty.f32(), utils::Vector{MemberAlign("val")})});
+    EXPECT_TRUE(r()->Resolve()) << r()->error();
+}
+
+TEST_F(StructMemberAttributeTest, Align_Attribute_ConstNegative) {
+    GlobalConst("val", ty.i32(), Expr(-2_i));
+
+    Structure("mystruct", utils::Vector{Member(
+                              "a", ty.f32(), utils::Vector{MemberAlign(Source{{12, 34}}, "val")})});
+    EXPECT_FALSE(r()->Resolve());
+    EXPECT_EQ(r()->error(),
+              R"(12:34 error: 'align' value must be a positive, power-of-two integer)");
+}
+
+TEST_F(StructMemberAttributeTest, Align_Attribute_ConstPowerOfTwo) {
+    GlobalConst("val", ty.i32(), Expr(3_i));
+
+    Structure("mystruct", utils::Vector{Member(
+                              "a", ty.f32(), utils::Vector{MemberAlign(Source{{12, 34}}, "val")})});
+    EXPECT_FALSE(r()->Resolve());
+    EXPECT_EQ(r()->error(),
+              R"(12:34 error: 'align' value must be a positive, power-of-two integer)");
+}
+
+TEST_F(StructMemberAttributeTest, Align_Attribute_ConstF32) {
+    GlobalConst("val", ty.f32(), Expr(1.23_f));
+
+    Structure("mystruct", utils::Vector{Member(
+                              "a", ty.f32(), utils::Vector{MemberAlign(Source{{12, 34}}, "val")})});
+    EXPECT_FALSE(r()->Resolve());
+    EXPECT_EQ(r()->error(), R"(12:34 error: 'align' must be an i32 value)");
+}
+
+TEST_F(StructMemberAttributeTest, Align_Attribute_ConstU32) {
+    GlobalConst("val", ty.u32(), Expr(2_u));
+
+    Structure("mystruct", utils::Vector{Member(
+                              "a", ty.f32(), utils::Vector{MemberAlign(Source{{12, 34}}, "val")})});
+    EXPECT_FALSE(r()->Resolve());
+    EXPECT_EQ(r()->error(), R"(12:34 error: 'align' must be an i32 value)");
+}
+
+TEST_F(StructMemberAttributeTest, Align_Attribute_ConstAInt) {
+    GlobalConst("val", Expr(2_a));
+
+    Structure("mystruct", utils::Vector{Member(
+                              "a", ty.f32(), utils::Vector{MemberAlign(Source{{12, 34}}, "val")})});
+    EXPECT_TRUE(r()->Resolve()) << r()->error();
+}
+
+TEST_F(StructMemberAttributeTest, Align_Attribute_ConstAFloat) {
+    GlobalConst("val", Expr(2.0_a));
+
+    Structure("mystruct", utils::Vector{Member(
+                              "a", ty.f32(), utils::Vector{MemberAlign(Source{{12, 34}}, "val")})});
+    EXPECT_FALSE(r()->Resolve());
+    EXPECT_EQ(r()->error(), R"(12:34 error: 'align' must be an i32 value)");
+}
+
+TEST_F(StructMemberAttributeTest, Align_Attribute_Var) {
+    GlobalVar(Source{{1, 2}}, "val", ty.f32(), ast::StorageClass::kPrivate, ast::Access::kUndefined,
+              Expr(1.23_f));
+
+    Structure(Source{{6, 4}}, "mystruct",
+              utils::Vector{Member(Source{{12, 5}}, "a", ty.f32(),
+                                   utils::Vector{MemberAlign(Expr(Source{{12, 35}}, "val"))})});
+    EXPECT_FALSE(r()->Resolve());
+    EXPECT_EQ(r()->error(), R"(12:35 error: var 'val' cannot be referenced at module-scope
+1:2 note: var 'val' declared here)");
+}
+
+TEST_F(StructMemberAttributeTest, Align_Attribute_Override) {
+    Override("val", ty.f32(), Expr(1.23_f));
+
+    Structure("mystruct", utils::Vector{Member(
+                              "a", ty.f32(), utils::Vector{MemberAlign(Source{{12, 34}}, "val")})});
+    EXPECT_FALSE(r()->Resolve());
+    EXPECT_EQ(r()->error(), R"(12:34 error: 'align' must be an i32 value)");
+}
+
 }  // namespace StructAndStructMemberTests
 
 using ArrayAttributeTest = TestWithParams;
diff --git a/src/tint/resolver/dependency_graph.cc b/src/tint/resolver/dependency_graph.cc
index 823dcad..0b391c5 100644
--- a/src/tint/resolver/dependency_graph.cc
+++ b/src/tint/resolver/dependency_graph.cc
@@ -182,6 +182,7 @@
             [&](const ast::Struct* str) {
                 Declare(str->name, str);
                 for (auto* member : str->members) {
+                    TraverseAttributes(member->attributes);
                     TraverseType(member->type);
                 }
             },
@@ -421,11 +422,16 @@
             TraverseExpression(wg->z);
             return;
         }
+        if (auto* align = attr->As<ast::StructMemberAlignAttribute>()) {
+            TraverseExpression(align->expr);
+            return;
+        }
+
         if (attr->IsAnyOf<ast::BindingAttribute, ast::BuiltinAttribute, ast::GroupAttribute,
                           ast::IdAttribute, ast::InternalAttribute, ast::InterpolateAttribute,
                           ast::InvariantAttribute, ast::LocationAttribute, ast::StageAttribute,
-                          ast::StrideAttribute, ast::StructMemberAlignAttribute,
-                          ast::StructMemberOffsetAttribute, ast::StructMemberSizeAttribute>()) {
+                          ast::StrideAttribute, ast::StructMemberOffsetAttribute,
+                          ast::StructMemberSizeAttribute>()) {
             return;
         }
 
diff --git a/src/tint/resolver/dependency_graph_test.cc b/src/tint/resolver/dependency_graph_test.cc
index 224d342..c9ffc91 100644
--- a/src/tint/resolver/dependency_graph_test.cc
+++ b/src/tint/resolver/dependency_graph_test.cc
@@ -1229,7 +1229,10 @@
 #define F add_use(func_decl, Expr(func_sym), __LINE__, "F()")
 
     Alias(Sym(), T);
-    Structure(Sym(), utils::Vector{Member(Sym(), T)});
+    Structure(Sym(),  //
+              utils::Vector{
+                  Member(Sym(), T, utils::Vector{MemberAlign(V)})  //
+              });
     GlobalVar(Sym(), T, V);
     GlobalConst(Sym(), T, V);
     Func(Sym(),                           //
diff --git a/src/tint/resolver/resolver.cc b/src/tint/resolver/resolver.cc
index ded0afa..3102292 100644
--- a/src/tint/resolver/resolver.cc
+++ b/src/tint/resolver/resolver.cc
@@ -2821,15 +2821,20 @@
                 if (!materialized) {
                     return nullptr;
                 }
+                if (!materialized->Type()->Is<sem::I32>()) {
+                    AddError("'align' must be an i32 value", a->source);
+                    return nullptr;
+                }
+
                 auto const_value = materialized->ConstantValue();
                 if (!const_value) {
-                    AddError("'align' must be constant expression", a->expr->source);
+                    AddError("'align' must be constant expression", a->source);
                     return nullptr;
                 }
                 auto value = const_value->As<AInt>();
 
                 if (value <= 0 || !utils::IsPowerOfTwo(value)) {
-                    AddError("align value must be a positive, power-of-two integer", a->source);
+                    AddError("'align' value must be a positive, power-of-two integer", a->source);
                     return nullptr;
                 }
                 align = const_value->As<u32>();
diff --git a/src/tint/resolver/storage_class_layout_validation_test.cc b/src/tint/resolver/storage_class_layout_validation_test.cc
index 91d0d5d..818a7d0 100644
--- a/src/tint/resolver/storage_class_layout_validation_test.cc
+++ b/src/tint/resolver/storage_class_layout_validation_test.cc
@@ -36,7 +36,7 @@
     Structure(Source{{12, 34}}, "S",
               utils::Vector{
                   Member("a", ty.f32(), utils::Vector{MemberSize(5_a)}),
-                  Member(Source{{34, 56}}, "b", ty.f32(), utils::Vector{MemberAlign(1_u)}),
+                  Member(Source{{34, 56}}, "b", ty.f32(), utils::Vector{MemberAlign(1_i)}),
               });
 
     GlobalVar(Source{{78, 90}}, "a", ty.type_name("S"), ast::StorageClass::kStorage, Group(0_a),
@@ -66,7 +66,7 @@
     Structure(Source{{12, 34}}, "S",
               utils::Vector{
                   Member("a", ty.f32(), utils::Vector{MemberSize(5_a)}),
-                  Member(Source{{34, 56}}, "b", ty.f32(), utils::Vector{MemberAlign(4_u)}),
+                  Member(Source{{34, 56}}, "b", ty.f32(), utils::Vector{MemberAlign(4_i)}),
               });
 
     GlobalVar(Source{{78, 90}}, "a", ty.type_name("S"), ast::StorageClass::kStorage, Group(0_a),
@@ -142,7 +142,7 @@
               utils::Vector{
                   Member("scalar", ty.f32()),
                   Member(Source{{56, 78}}, "inner", ty.type_name("Inner"),
-                         utils::Vector{MemberAlign(16_u)}),
+                         utils::Vector{MemberAlign(16_i)}),
               });
 
     GlobalVar(Source{{78, 90}}, "a", ty.type_name("Outer"), ast::StorageClass::kUniform, Group(0_a),
@@ -201,7 +201,7 @@
               utils::Vector{
                   Member("scalar", ty.f32()),
                   Member(Source{{34, 56}}, "inner", ty.type_name("Inner"),
-                         utils::Vector{MemberAlign(16_u)}),
+                         utils::Vector{MemberAlign(16_i)}),
               });
 
     GlobalVar(Source{{78, 90}}, "a", ty.type_name("Outer"), ast::StorageClass::kUniform, Group(0_a),
@@ -227,7 +227,7 @@
 
     Structure(Source{{12, 34}}, "Inner",
               utils::Vector{
-                  Member("scalar", ty.i32(), utils::Vector{MemberAlign(1_u), MemberSize(5_a)}),
+                  Member("scalar", ty.i32(), utils::Vector{MemberAlign(1_i), MemberSize(5_a)}),
               });
 
     Structure(Source{{34, 56}}, "Outer",
@@ -279,7 +279,7 @@
                   Member("a", ty.i32()),
                   Member("b", ty.i32()),
                   Member("c", ty.i32()),
-                  Member("scalar", ty.i32(), utils::Vector{MemberAlign(1_u), MemberSize(5_a)}),
+                  Member("scalar", ty.i32(), utils::Vector{MemberAlign(1_i), MemberSize(5_a)}),
               });
 
     Structure(Source{{34, 56}}, "Outer",
@@ -327,13 +327,13 @@
 
     Structure(Source{{12, 34}}, "Inner",
               utils::Vector{
-                  Member("scalar", ty.i32(), utils::Vector{MemberAlign(1_u), MemberSize(5_a)}),
+                  Member("scalar", ty.i32(), utils::Vector{MemberAlign(1_i), MemberSize(5_a)}),
               });
 
     Structure(Source{{34, 56}}, "Outer",
               utils::Vector{
                   Member(Source{{56, 78}}, "inner", ty.type_name("Inner")),
-                  Member(Source{{78, 90}}, "scalar", ty.i32(), utils::Vector{MemberAlign(16_u)}),
+                  Member(Source{{78, 90}}, "scalar", ty.i32(), utils::Vector{MemberAlign(16_i)}),
               });
 
     GlobalVar(Source{{22, 34}}, "a", ty.type_name("Outer"), ast::StorageClass::kUniform, Group(0_a),
@@ -551,7 +551,7 @@
     Structure(
         Source{{12, 34}}, "S",
         utils::Vector{Member("a", ty.f32(), utils::Vector{MemberSize(5_a)}),
-                      Member(Source{{34, 56}}, "b", ty.f32(), utils::Vector{MemberAlign(1_u)})});
+                      Member(Source{{34, 56}}, "b", ty.f32(), utils::Vector{MemberAlign(1_i)})});
     GlobalVar(Source{{78, 90}}, "a", ty.type_name("S"), ast::StorageClass::kPushConstant);
 
     ASSERT_FALSE(r()->Resolve());
@@ -576,7 +576,7 @@
     // var<push_constant> a : S;
     Enable(ast::Extension::kChromiumExperimentalPushConstant);
     Structure("S", utils::Vector{Member("a", ty.f32(), utils::Vector{MemberSize(5_a)}),
-                                 Member("b", ty.f32(), utils::Vector{MemberAlign(4_u)})});
+                                 Member("b", ty.f32(), utils::Vector{MemberAlign(4_i)})});
     GlobalVar("a", ty.type_name("S"), ast::StorageClass::kPushConstant);
 
     ASSERT_TRUE(r()->Resolve()) << r()->error();
diff --git a/src/tint/resolver/struct_layout_test.cc b/src/tint/resolver/struct_layout_test.cc
index 5b5ab68..1e5ec45 100644
--- a/src/tint/resolver/struct_layout_test.cc
+++ b/src/tint/resolver/struct_layout_test.cc
@@ -498,15 +498,15 @@
 
 TEST_F(ResolverStructLayoutTest, AlignAttributes) {
     auto* inner = Structure("Inner", utils::Vector{
-                                         Member("a", ty.f32(), utils::Vector{MemberAlign(8_u)}),
-                                         Member("b", ty.f32(), utils::Vector{MemberAlign(16_u)}),
-                                         Member("c", ty.f32(), utils::Vector{MemberAlign(4_u)}),
+                                         Member("a", ty.f32(), utils::Vector{MemberAlign(8_i)}),
+                                         Member("b", ty.f32(), utils::Vector{MemberAlign(16_i)}),
+                                         Member("c", ty.f32(), utils::Vector{MemberAlign(4_i)}),
                                      });
     auto* s = Structure("S", utils::Vector{
-                                 Member("a", ty.f32(), utils::Vector{MemberAlign(4_u)}),
-                                 Member("b", ty.u32(), utils::Vector{MemberAlign(8_u)}),
+                                 Member("a", ty.f32(), utils::Vector{MemberAlign(4_i)}),
+                                 Member("b", ty.u32(), utils::Vector{MemberAlign(8_i)}),
                                  Member("c", ty.Of(inner)),
-                                 Member("d", ty.i32(), utils::Vector{MemberAlign(32_u)}),
+                                 Member("d", ty.i32(), utils::Vector{MemberAlign(32_i)}),
                              });
 
     ASSERT_TRUE(r()->Resolve()) << r()->error();
@@ -536,7 +536,7 @@
 
 TEST_F(ResolverStructLayoutTest, StructWithLotsOfPadding) {
     auto* s = Structure("S", utils::Vector{
-                                 Member("a", ty.i32(), utils::Vector{MemberAlign(1024_u)}),
+                                 Member("a", ty.i32(), utils::Vector{MemberAlign(1024_i)}),
                              });
 
     ASSERT_TRUE(r()->Resolve()) << r()->error();
diff --git a/src/tint/resolver/validation_test.cc b/src/tint/resolver/validation_test.cc
index 90b1664..825fbc9 100644
--- a/src/tint/resolver/validation_test.cc
+++ b/src/tint/resolver/validation_test.cc
@@ -1237,22 +1237,31 @@
     EXPECT_TRUE(r()->Resolve());
 }
 
-TEST_F(ResolverValidationTest, NonPOTStructMemberAlignAttribute) {
+TEST_F(ResolverValidationTest, NegativeStructMemberAlignAttribute) {
     Structure("S", utils::Vector{
-                       Member("a", ty.f32(), utils::Vector{MemberAlign(Source{{12, 34}}, 3_u)}),
+                       Member("a", ty.f32(), utils::Vector{MemberAlign(Source{{12, 34}}, -2_i)}),
                    });
 
     EXPECT_FALSE(r()->Resolve());
-    EXPECT_EQ(r()->error(), "12:34 error: align value must be a positive, power-of-two integer");
+    EXPECT_EQ(r()->error(), "12:34 error: 'align' value must be a positive, power-of-two integer");
+}
+
+TEST_F(ResolverValidationTest, NonPOTStructMemberAlignAttribute) {
+    Structure("S", utils::Vector{
+                       Member("a", ty.f32(), utils::Vector{MemberAlign(Source{{12, 34}}, 3_i)}),
+                   });
+
+    EXPECT_FALSE(r()->Resolve());
+    EXPECT_EQ(r()->error(), "12:34 error: 'align' value must be a positive, power-of-two integer");
 }
 
 TEST_F(ResolverValidationTest, ZeroStructMemberAlignAttribute) {
     Structure("S", utils::Vector{
-                       Member("a", ty.f32(), utils::Vector{MemberAlign(Source{{12, 34}}, 0_u)}),
+                       Member("a", ty.f32(), utils::Vector{MemberAlign(Source{{12, 34}}, 0_i)}),
                    });
 
     EXPECT_FALSE(r()->Resolve());
-    EXPECT_EQ(r()->error(), "12:34 error: align value must be a positive, power-of-two integer");
+    EXPECT_EQ(r()->error(), "12:34 error: 'align' value must be a positive, power-of-two integer");
 }
 
 TEST_F(ResolverValidationTest, ZeroStructMemberSizeAttribute) {
@@ -1279,7 +1288,7 @@
 TEST_F(ResolverValidationTest, OffsetAndAlignAttribute) {
     Structure("S", utils::Vector{
                        Member(Source{{12, 34}}, "a", ty.f32(),
-                              utils::Vector{MemberOffset(0_a), MemberAlign(4_u)}),
+                              utils::Vector{MemberOffset(0_a), MemberAlign(4_i)}),
                    });
 
     EXPECT_FALSE(r()->Resolve());
@@ -1291,7 +1300,7 @@
 TEST_F(ResolverValidationTest, OffsetAndAlignAndSizeAttribute) {
     Structure("S", utils::Vector{
                        Member(Source{{12, 34}}, "a", ty.f32(),
-                              utils::Vector{MemberOffset(0_a), MemberAlign(4_u), MemberSize(4_a)}),
+                              utils::Vector{MemberOffset(0_a), MemberAlign(4_i), MemberSize(4_a)}),
                    });
 
     EXPECT_FALSE(r()->Resolve());
diff --git a/src/tint/transform/std140.cc b/src/tint/transform/std140.cc
index 1f495f0..66857bc 100644
--- a/src/tint/transform/std140.cc
+++ b/src/tint/transform/std140.cc
@@ -460,7 +460,7 @@
                 // The matrix was @align() annotated with a larger alignment
                 // than the natural alignment for the matrix. This extra padding
                 // needs to be applied to the first column vector.
-                attributes.Push(b.MemberAlign(u32(align)));
+                attributes.Push(b.MemberAlign(i32(align)));
             }
             if ((i == num_columns - 1) && mat->Size() != size) {
                 // The matrix was @size() annotated with a larger size than the
diff --git a/src/tint/transform/std140_test.cc b/src/tint/transform/std140_test.cc
index 97936ad..6e0b170 100644
--- a/src/tint/transform/std140_test.cc
+++ b/src/tint/transform/std140_test.cc
@@ -200,7 +200,7 @@
 
 struct S_std140 {
   before : i32,
-  @align(128u)
+  @align(128i)
   m_0 : vec2<f32>,
   m_1 : vec2<f32>,
   m_2 : vec2<f32>,
@@ -272,7 +272,7 @@
 
 struct S_std140 {
   before : i32,
-  @align(128u)
+  @align(128i)
   m_0 : vec2<f32>,
   m_1 : vec2<f32>,
   @size(112)
diff --git a/src/tint/writer/glsl/generator_impl_storage_buffer_test.cc b/src/tint/writer/glsl/generator_impl_storage_buffer_test.cc
index f6f127f..78d5859 100644
--- a/src/tint/writer/glsl/generator_impl_storage_buffer_test.cc
+++ b/src/tint/writer/glsl/generator_impl_storage_buffer_test.cc
@@ -33,9 +33,9 @@
     // @group(0) @binding(0) var<storage, read_write> nephews : Nephews;
     auto* nephews = ctx->Structure(
         "Nephews", utils::Vector{
-                       ctx->Member("huey", ctx->ty.f32(), utils::Vector{ctx->MemberAlign(256_u)}),
-                       ctx->Member("dewey", ctx->ty.f32(), utils::Vector{ctx->MemberAlign(256_u)}),
-                       ctx->Member("louie", ctx->ty.f32(), utils::Vector{ctx->MemberAlign(256_u)}),
+                       ctx->Member("huey", ctx->ty.f32(), utils::Vector{ctx->MemberAlign(256_i)}),
+                       ctx->Member("dewey", ctx->ty.f32(), utils::Vector{ctx->MemberAlign(256_i)}),
+                       ctx->Member("louie", ctx->ty.f32(), utils::Vector{ctx->MemberAlign(256_i)}),
                    });
     ctx->GlobalVar("nephews", ctx->ty.Of(nephews), ast::StorageClass::kStorage, ctx->Binding(0_a),
                    ctx->Group(0_a));
diff --git a/src/tint/writer/msl/generator_impl_type_test.cc b/src/tint/writer/msl/generator_impl_type_test.cc
index c8f4f6d..a8d9fc6 100644
--- a/src/tint/writer/msl/generator_impl_type_test.cc
+++ b/src/tint/writer/msl/generator_impl_type_test.cc
@@ -255,7 +255,7 @@
     auto* s = Structure(
         "S", utils::Vector{
                  Member("a", ty.i32(), utils::Vector{MemberSize(32_a)}),
-                 Member("b", ty.f32(), utils::Vector{MemberAlign(128_u), MemberSize(128_a)}),
+                 Member("b", ty.f32(), utils::Vector{MemberAlign(128_i), MemberSize(128_a)}),
                  Member("c", ty.vec2<f32>()),
                  Member("d", ty.u32()),
                  Member("e", ty.vec3<f32>()),
@@ -372,7 +372,7 @@
     auto* inner_x =
         Structure("inner_x", utils::Vector{
                                  Member("a", ty.i32()),
-                                 Member("b", ty.f32(), utils::Vector{MemberAlign(512_u)}),
+                                 Member("b", ty.f32(), utils::Vector{MemberAlign(512_i)}),
                              });
 
     // inner_y: size(516), align(4)
@@ -460,7 +460,7 @@
     // inner: size(1024), align(512)
     auto* inner = Structure("inner", utils::Vector{
                                          Member("a", ty.i32()),
-                                         Member("b", ty.f32(), utils::Vector{MemberAlign(512_u)}),
+                                         Member("b", ty.f32(), utils::Vector{MemberAlign(512_i)}),
                                      });
 
     // array_x: size(28), align(4)
@@ -598,7 +598,7 @@
                                  // uses symbols tint_pad_[0..9] and tint_pad_[20..35]
                                  Member("tint_pad_2", ty.i32(), utils::Vector{MemberSize(32_a)}),
                                  Member("tint_pad_20", ty.f32(),
-                                        utils::Vector{MemberAlign(128_u), MemberSize(128_u)}),
+                                        utils::Vector{MemberAlign(128_i), MemberSize(128_u)}),
                                  Member("tint_pad_33", ty.vec2<f32>()),
                                  Member("tint_pad_1", ty.u32()),
                                  Member("tint_pad_3", ty.vec3<f32>()),
diff --git a/src/tint/writer/spirv/builder_type_test.cc b/src/tint/writer/spirv/builder_type_test.cc
index 9b61268..ea530d2 100644
--- a/src/tint/writer/spirv/builder_type_test.cc
+++ b/src/tint/writer/spirv/builder_type_test.cc
@@ -336,7 +336,7 @@
 TEST_F(BuilderTest_Type, GenerateStruct_DecoratedMembers) {
     auto* s = Structure("S", utils::Vector{
                                  Member("a", ty.f32()),
-                                 Member("b", ty.f32(), utils::Vector{MemberAlign(8_u)}),
+                                 Member("b", ty.f32(), utils::Vector{MemberAlign(8_i)}),
                              });
 
     spirv::Builder& b = Build();