diff --git a/BUILD.gn b/BUILD.gn
index bc65b11..39d66df 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -656,6 +656,7 @@
     "src/reader/spirv/function_glsl_std_450_test.cc",
     "src/reader/spirv/function_logical_test.cc",
     "src/reader/spirv/function_memory_test.cc",
+    "src/reader/spirv/function_misc_test.cc",
     "src/reader/spirv/function_var_test.cc",
     "src/reader/spirv/namer_test.cc",
     "src/reader/spirv/parser_impl_convert_member_decoration_test.cc",
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index e046cda..6c1138b 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -325,8 +325,9 @@
     reader/spirv/function_decl_test.cc
     reader/spirv/function_glsl_std_450_test.cc
     reader/spirv/function_logical_test.cc
-    reader/spirv/function_var_test.cc
     reader/spirv/function_memory_test.cc
+    reader/spirv/function_misc_test.cc
+    reader/spirv/function_var_test.cc
     reader/spirv/namer_test.cc
     reader/spirv/parser_impl_convert_member_decoration_test.cc
     reader/spirv/parser_impl_convert_type_test.cc
diff --git a/src/reader/spirv/function.cc b/src/reader/spirv/function.cc
index 9d3d526..d92862c 100644
--- a/src/reader/spirv/function.cc
+++ b/src/reader/spirv/function.cc
@@ -2533,16 +2533,21 @@
   if (opcode == SpvOpVectorShuffle) {
     return MakeVectorShuffle(inst);
   }
+
   if (opcode == SpvOpConvertSToF || opcode == SpvOpConvertUToF ||
       opcode == SpvOpConvertFToS || opcode == SpvOpConvertFToU) {
     return MakeNumericConversion(inst);
   }
 
+  if (opcode == SpvOpUndef) {
+    // Replace undef with the null value.
+    return {ast_type, parser_impl_.MakeNullValue(ast_type)};
+  }
+
   // builtin readonly function
   // glsl.std.450 readonly function
 
   // Instructions:
-  //    OpUndef
   //    OpSatConvertSToU // Only in Kernel (OpenCL), not in WebGPU
   //    OpSatConvertUToS // Only in Kernel (OpenCL), not in WebGPU
   //    OpUConvert // Only needed when multiple widths supported
@@ -2557,7 +2562,6 @@
   //    OpArrayLength
   //    OpVectorExtractDynamic
   //    OpVectorInsertDynamic
-  //    OpCompositeExtract
   //    OpCompositeInsert
 
   return {};
diff --git a/src/reader/spirv/function_misc_test.cc b/src/reader/spirv/function_misc_test.cc
new file mode 100644
index 0000000..7e1e5f8
--- /dev/null
+++ b/src/reader/spirv/function_misc_test.cc
@@ -0,0 +1,286 @@
+// Copyright 2020 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <string>
+#include <vector>
+
+#include "gmock/gmock.h"
+#include "src/reader/spirv/function.h"
+#include "src/reader/spirv/parser_impl.h"
+#include "src/reader/spirv/parser_impl_test_helper.h"
+#include "src/reader/spirv/spirv_tools_helpers_test.h"
+
+namespace tint {
+namespace reader {
+namespace spirv {
+namespace {
+
+using ::testing::HasSubstr;
+
+std::string CommonTypes() {
+  return R"(
+  %void = OpTypeVoid
+  %voidfn = OpTypeFunction %void
+
+  %bool = OpTypeBool
+  %uint = OpTypeInt 32 0
+  %int = OpTypeInt 32 1
+  %float = OpTypeFloat 32
+
+  %v2uint = OpTypeVector %uint 2
+  %v2int = OpTypeVector %int 2
+  %v2float = OpTypeVector %float 2
+)";
+}
+
+using SpvParserTestMiscInstruction = SpvParserTest;
+
+TEST_F(SpvParserTestMiscInstruction, OpUndef_InFunction_Scalar) {
+  const auto assembly = CommonTypes() + R"(
+     %100 = OpFunction %void None %voidfn
+     %entry = OpLabel
+     %1 = OpUndef %bool
+     %2 = OpUndef %uint
+     %3 = OpUndef %int
+     %4 = OpUndef %float
+
+     %11 = OpCopyObject %bool %1
+     %12 = OpCopyObject %uint %2
+     %13 = OpCopyObject %int %3
+     %14 = OpCopyObject %float %4
+     OpReturn
+     OpFunctionEnd
+)";
+  auto* p = parser(test::Assemble(assembly));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions()) << assembly;
+  FunctionEmitter fe(p, *spirv_function(100));
+  EXPECT_TRUE(fe.EmitBody()) << p->error();
+  EXPECT_THAT(ToString(fe.ast_body()), HasSubstr(R"(VariableDeclStatement{
+  Variable{
+    x_11
+    none
+    __bool
+    {
+      ScalarConstructor{false}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    x_12
+    none
+    __u32
+    {
+      ScalarConstructor{0}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    x_13
+    none
+    __i32
+    {
+      ScalarConstructor{0}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    x_14
+    none
+    __f32
+    {
+      ScalarConstructor{0.000000}
+    }
+  }
+})")) << ToString(fe.ast_body());
+}
+
+TEST_F(SpvParserTestMiscInstruction, OpUndef_InFunction_Vector) {
+  const auto assembly = CommonTypes() + R"(
+     %100 = OpFunction %void None %voidfn
+     %entry = OpLabel
+     %1 = OpUndef %v2uint
+     %2 = OpUndef %v2int
+     %3 = OpUndef %v2float
+
+     %11 = OpCopyObject %v2uint %1
+     %12 = OpCopyObject %v2int %2
+     %13 = OpCopyObject %v2float %3
+     OpReturn
+     OpFunctionEnd
+)";
+  auto* p = parser(test::Assemble(assembly));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions()) << assembly;
+  FunctionEmitter fe(p, *spirv_function(100));
+  EXPECT_TRUE(fe.EmitBody()) << p->error();
+  EXPECT_THAT(ToString(fe.ast_body()), HasSubstr(R"(VariableDeclStatement{
+  Variable{
+    x_11
+    none
+    __vec_2__u32
+    {
+      TypeConstructor{
+        __vec_2__u32
+        ScalarConstructor{0}
+        ScalarConstructor{0}
+      }
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    x_12
+    none
+    __vec_2__i32
+    {
+      TypeConstructor{
+        __vec_2__i32
+        ScalarConstructor{0}
+        ScalarConstructor{0}
+      }
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    x_13
+    none
+    __vec_2__f32
+    {
+      TypeConstructor{
+        __vec_2__f32
+        ScalarConstructor{0.000000}
+        ScalarConstructor{0.000000}
+      }
+    }
+  }
+})")) << ToString(fe.ast_body());
+}
+
+TEST_F(SpvParserTestMiscInstruction, OpUndef_InFunction_Matrix) {
+  const auto assembly = CommonTypes() + R"(
+     %mat = OpTypeMatrix %v2float 2
+
+     %100 = OpFunction %void None %voidfn
+     %entry = OpLabel
+     %1 = OpUndef %mat
+
+     %11 = OpCopyObject %mat %1
+     OpReturn
+     OpFunctionEnd
+)";
+  auto* p = parser(test::Assemble(assembly));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions()) << assembly;
+  FunctionEmitter fe(p, *spirv_function(100));
+  EXPECT_TRUE(fe.EmitBody()) << p->error();
+  EXPECT_THAT(ToString(fe.ast_body()), HasSubstr(R"(VariableDeclStatement{
+  Variable{
+    x_11
+    none
+    __mat_2_2__f32
+    {
+      TypeConstructor{
+        __mat_2_2__f32
+        TypeConstructor{
+          __vec_2__f32
+          ScalarConstructor{0.000000}
+          ScalarConstructor{0.000000}
+        }
+        TypeConstructor{
+          __vec_2__f32
+          ScalarConstructor{0.000000}
+          ScalarConstructor{0.000000}
+        }
+      }
+    }
+  }
+})")) << ToString(fe.ast_body());
+}
+
+TEST_F(SpvParserTestMiscInstruction, OpUndef_InFunction_Array) {
+  const auto assembly = CommonTypes() + R"(
+     %uint_2 = OpConstant %uint 2
+     %arr = OpTypeArray %uint %uint_2
+
+     %100 = OpFunction %void None %voidfn
+     %entry = OpLabel
+     %1 = OpUndef %arr
+
+     %11 = OpCopyObject %arr %1
+     OpReturn
+     OpFunctionEnd
+)";
+  auto* p = parser(test::Assemble(assembly));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions()) << assembly;
+  FunctionEmitter fe(p, *spirv_function(100));
+  EXPECT_TRUE(fe.EmitBody()) << p->error();
+  EXPECT_THAT(ToString(fe.ast_body()), HasSubstr(R"(VariableDeclStatement{
+  Variable{
+    x_11
+    none
+    __array__u32_2
+    {
+      TypeConstructor{
+        __array__u32_2
+        ScalarConstructor{0}
+        ScalarConstructor{0}
+      }
+    }
+  }
+})")) << ToString(fe.ast_body());
+}
+
+TEST_F(SpvParserTestMiscInstruction, OpUndef_InFunction_Struct) {
+  const auto assembly = CommonTypes() + R"(
+     %strct = OpTypeStruct %bool %uint %int %float
+
+     %100 = OpFunction %void None %voidfn
+     %entry = OpLabel
+     %1 = OpUndef %strct
+
+     %11 = OpCopyObject %strct %1
+     OpReturn
+     OpFunctionEnd
+)";
+  auto* p = parser(test::Assemble(assembly));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions()) << assembly;
+  FunctionEmitter fe(p, *spirv_function(100));
+  EXPECT_TRUE(fe.EmitBody()) << p->error();
+  EXPECT_THAT(ToString(fe.ast_body()), HasSubstr(R"(VariableDeclStatement{
+  Variable{
+    x_11
+    none
+    __alias_S__struct_S
+    {
+      TypeConstructor{
+        __alias_S__struct_S
+        ScalarConstructor{false}
+        ScalarConstructor{0}
+        ScalarConstructor{0}
+        ScalarConstructor{0.000000}
+      }
+    }
+  }
+})")) << ToString(fe.ast_body());
+}
+
+// TODO(dneto): OpNop
+// TODO(dneto): OpSizeof : requires Kernel (OpenCL)
+
+}  // namespace
+}  // namespace spirv
+}  // namespace reader
+}  // namespace tint
diff --git a/src/reader/spirv/parser_impl.cc b/src/reader/spirv/parser_impl.cc
index 5d53d6d..4ad72ee 100644
--- a/src/reader/spirv/parser_impl.cc
+++ b/src/reader/spirv/parser_impl.cc
@@ -890,6 +890,12 @@
   if (original_ast_type == nullptr) {
     return {};
   }
+
+  if (inst->opcode() == SpvOpUndef) {
+    // Remap undef to null.
+    return {original_ast_type, MakeNullValue(original_ast_type)};
+  }
+
   // TODO(dneto): Handle spec constants too?
   const auto* spirv_const = constant_mgr_->FindDeclaredConstant(id);
   if (spirv_const == nullptr) {
diff --git a/src/reader/spirv/parser_impl_module_var_test.cc b/src/reader/spirv/parser_impl_module_var_test.cc
index ffbe3cc..b0c9d00 100644
--- a/src/reader/spirv/parser_impl_module_var_test.cc
+++ b/src/reader/spirv/parser_impl_module_var_test.cc
@@ -293,6 +293,55 @@
   })"));
 }
 
+TEST_F(SpvParserTest, ModuleScopeVar_ScalarUndefInitializers) {
+  auto* p = parser(test::Assemble(CommonTypes() + R"(
+     %undef_bool = OpUndef %bool
+     %undef_int = OpUndef %int
+     %undef_uint = OpUndef %uint
+     %undef_float = OpUndef %float
+
+     %1 = OpVariable %ptr_bool Private %undef_bool
+     %2 = OpVariable %ptr_int Private %undef_int
+     %3 = OpVariable %ptr_uint Private %undef_uint
+     %4 = OpVariable %ptr_float Private %undef_float
+  )"));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions()) << p->error();
+  EXPECT_TRUE(p->error().empty());
+  const auto module_str = p->module().to_str();
+  EXPECT_THAT(module_str, HasSubstr(R"(Variable{
+    x_1
+    private
+    __bool
+    {
+      ScalarConstructor{false}
+    }
+  }
+  Variable{
+    x_2
+    private
+    __i32
+    {
+      ScalarConstructor{0}
+    }
+  }
+  Variable{
+    x_3
+    private
+    __u32
+    {
+      ScalarConstructor{0}
+    }
+  }
+  Variable{
+    x_4
+    private
+    __f32
+    {
+      ScalarConstructor{0.000000}
+    }
+  })"));
+}
+
 TEST_F(SpvParserTest, ModuleScopeVar_VectorInitializer) {
   auto* p = parser(test::Assemble(CommonTypes() + R"(
      %ptr = OpTypePointer Private %v2float
@@ -340,6 +389,29 @@
   })"));
 }
 
+TEST_F(SpvParserTest, ModuleScopeVar_VectorBoolUndefInitializer) {
+  auto* p = parser(test::Assemble(CommonTypes() + R"(
+     %ptr = OpTypePointer Private %v2bool
+     %const = OpUndef %v2bool
+     %200 = OpVariable %ptr Private %const
+  )"));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions());
+  EXPECT_TRUE(p->error().empty());
+  const auto module_str = p->module().to_str();
+  EXPECT_THAT(module_str, HasSubstr(R"(Variable{
+    x_200
+    private
+    __vec_2__bool
+    {
+      TypeConstructor{
+        __vec_2__bool
+        ScalarConstructor{false}
+        ScalarConstructor{false}
+      }
+    }
+  })"));
+}
+
 TEST_F(SpvParserTest, ModuleScopeVar_VectorUintNullInitializer) {
   auto* p = parser(test::Assemble(CommonTypes() + R"(
      %ptr = OpTypePointer Private %v2uint
@@ -363,6 +435,29 @@
   })"));
 }
 
+TEST_F(SpvParserTest, ModuleScopeVar_VectorUintUndefInitializer) {
+  auto* p = parser(test::Assemble(CommonTypes() + R"(
+     %ptr = OpTypePointer Private %v2uint
+     %const = OpUndef %v2uint
+     %200 = OpVariable %ptr Private %const
+  )"));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions());
+  EXPECT_TRUE(p->error().empty());
+  const auto module_str = p->module().to_str();
+  EXPECT_THAT(module_str, HasSubstr(R"(Variable{
+    x_200
+    private
+    __vec_2__u32
+    {
+      TypeConstructor{
+        __vec_2__u32
+        ScalarConstructor{0}
+        ScalarConstructor{0}
+      }
+    }
+  })"));
+}
+
 TEST_F(SpvParserTest, ModuleScopeVar_VectorIntNullInitializer) {
   auto* p = parser(test::Assemble(CommonTypes() + R"(
      %ptr = OpTypePointer Private %v2int
@@ -386,6 +481,29 @@
   })"));
 }
 
+TEST_F(SpvParserTest, ModuleScopeVar_VectorIntUndefInitializer) {
+  auto* p = parser(test::Assemble(CommonTypes() + R"(
+     %ptr = OpTypePointer Private %v2int
+     %const = OpUndef %v2int
+     %200 = OpVariable %ptr Private %const
+  )"));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions());
+  EXPECT_TRUE(p->error().empty());
+  const auto module_str = p->module().to_str();
+  EXPECT_THAT(module_str, HasSubstr(R"(Variable{
+    x_200
+    private
+    __vec_2__i32
+    {
+      TypeConstructor{
+        __vec_2__i32
+        ScalarConstructor{0}
+        ScalarConstructor{0}
+      }
+    }
+  })"));
+}
+
 TEST_F(SpvParserTest, ModuleScopeVar_VectorFloatNullInitializer) {
   auto* p = parser(test::Assemble(CommonTypes() + R"(
      %ptr = OpTypePointer Private %v2float
@@ -409,6 +527,29 @@
   })"));
 }
 
+TEST_F(SpvParserTest, ModuleScopeVar_VectorFloatUndefInitializer) {
+  auto* p = parser(test::Assemble(CommonTypes() + R"(
+     %ptr = OpTypePointer Private %v2float
+     %const = OpUndef %v2float
+     %200 = OpVariable %ptr Private %const
+  )"));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions());
+  EXPECT_TRUE(p->error().empty());
+  const auto module_str = p->module().to_str();
+  EXPECT_THAT(module_str, HasSubstr(R"(Variable{
+    x_200
+    private
+    __vec_2__f32
+    {
+      TypeConstructor{
+        __vec_2__f32
+        ScalarConstructor{0.000000}
+        ScalarConstructor{0.000000}
+      }
+    }
+  })"));
+}
+
 TEST_F(SpvParserTest, ModuleScopeVar_MatrixInitializer) {
   auto* p = parser(test::Assemble(CommonTypes() + R"(
      %ptr = OpTypePointer Private %m3v2float
@@ -487,6 +628,42 @@
   })"));
 }
 
+TEST_F(SpvParserTest, ModuleScopeVar_MatrixUndefInitializer) {
+  auto* p = parser(test::Assemble(CommonTypes() + R"(
+     %ptr = OpTypePointer Private %m3v2float
+     %const = OpUndef %m3v2float
+     %200 = OpVariable %ptr Private %const
+  )"));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions());
+  EXPECT_TRUE(p->error().empty());
+  const auto module_str = p->module().to_str();
+  EXPECT_THAT(module_str, HasSubstr(R"(Variable{
+    x_200
+    private
+    __mat_2_3__f32
+    {
+      TypeConstructor{
+        __mat_2_3__f32
+        TypeConstructor{
+          __vec_2__f32
+          ScalarConstructor{0.000000}
+          ScalarConstructor{0.000000}
+        }
+        TypeConstructor{
+          __vec_2__f32
+          ScalarConstructor{0.000000}
+          ScalarConstructor{0.000000}
+        }
+        TypeConstructor{
+          __vec_2__f32
+          ScalarConstructor{0.000000}
+          ScalarConstructor{0.000000}
+        }
+      }
+    }
+  })"));
+}
+
 TEST_F(SpvParserTest, ModuleScopeVar_ArrayInitializer) {
   auto* p = parser(test::Assemble(CommonTypes() + R"(
      %ptr = OpTypePointer Private %arr2uint
@@ -534,6 +711,29 @@
   })"));
 }
 
+TEST_F(SpvParserTest, ModuleScopeVar_ArrayUndefInitializer) {
+  auto* p = parser(test::Assemble(CommonTypes() + R"(
+     %ptr = OpTypePointer Private %arr2uint
+     %const = OpUndef %arr2uint
+     %200 = OpVariable %ptr Private %const
+  )"));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions());
+  EXPECT_TRUE(p->error().empty());
+  const auto module_str = p->module().to_str();
+  EXPECT_THAT(module_str, HasSubstr(R"(Variable{
+    x_200
+    private
+    __array__u32_2
+    {
+      TypeConstructor{
+        __array__u32_2
+        ScalarConstructor{0}
+        ScalarConstructor{0}
+      }
+    }
+  })"));
+}
+
 TEST_F(SpvParserTest, ModuleScopeVar_StructInitializer) {
   auto* p = parser(test::Assemble(CommonTypes() + R"(
      %ptr = OpTypePointer Private %strct
@@ -594,6 +794,35 @@
       << module_str;
 }
 
+TEST_F(SpvParserTest, ModuleScopeVar_StructUndefInitializer) {
+  auto* p = parser(test::Assemble(CommonTypes() + R"(
+     %ptr = OpTypePointer Private %strct
+     %const = OpUndef %strct
+     %200 = OpVariable %ptr Private %const
+  )"));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions()) << p->error();
+  EXPECT_TRUE(p->error().empty());
+  const auto module_str = p->module().to_str();
+  EXPECT_THAT(module_str, HasSubstr(R"(Variable{
+    x_200
+    private
+    __alias_S__struct_S
+    {
+      TypeConstructor{
+        __alias_S__struct_S
+        ScalarConstructor{0}
+        ScalarConstructor{0.000000}
+        TypeConstructor{
+          __array__u32_2
+          ScalarConstructor{0}
+          ScalarConstructor{0}
+        }
+      }
+    }
+  })"))
+      << module_str;
+}
+
 }  // namespace
 }  // namespace spirv
 }  // namespace reader