diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 52c53c6..86166c6 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -248,6 +248,7 @@
   ast/unary_derivative_expression_test.cc
   ast/unary_method_expression_test.cc
   ast/unary_op_expression_test.cc
+  ast/unless_statement_test.cc
   ast/variable_test.cc
   reader/wgsl/lexer_test.cc
   reader/wgsl/parser_test.cc
diff --git a/src/ast/unless_statement.cc b/src/ast/unless_statement.cc
index 7f591b0..10f287d 100644
--- a/src/ast/unless_statement.cc
+++ b/src/ast/unless_statement.cc
@@ -17,6 +17,8 @@
 namespace tint {
 namespace ast {
 
+UnlessStatement::UnlessStatement() : Statement() {}
+
 UnlessStatement::UnlessStatement(std::unique_ptr<Expression> condition,
                                  std::vector<std::unique_ptr<Statement>> body)
     : Statement(), condition_(std::move(condition)), body_(std::move(body)) {}
@@ -31,22 +33,37 @@
 UnlessStatement::~UnlessStatement() = default;
 
 bool UnlessStatement::IsValid() const {
-  return condition_ != nullptr;
+  if (condition_ == nullptr || !condition_->IsValid()) {
+    return false;
+  }
+  for (const auto& stmt : body_) {
+    if (stmt == nullptr || !stmt->IsValid()) {
+      return false;
+    }
+  }
+  return true;
 }
 
 void UnlessStatement::to_str(std::ostream& out, size_t indent) const {
   make_indent(out, indent);
   out << "Unless{" << std::endl;
 
-  condition_->to_str(out, indent + 2);
-  make_indent(out, indent);
+  make_indent(out, indent + 2);
+  out << "(" << std::endl;
+
+  condition_->to_str(out, indent + 4);
+
+  make_indent(out, indent + 2);
+  out << ")" << std::endl;
+
+  make_indent(out, indent + 2);
   out << "{" << std::endl;
 
   for (const auto& stmt : body_)
     stmt->to_str(out, indent + 4);
 
   make_indent(out, indent + 2);
-  out << "}";
+  out << "}" << std::endl;
 
   make_indent(out, indent);
   out << "}" << std::endl;
diff --git a/src/ast/unless_statement.h b/src/ast/unless_statement.h
index bafbb43..718eded 100644
--- a/src/ast/unless_statement.h
+++ b/src/ast/unless_statement.h
@@ -29,6 +29,8 @@
 class UnlessStatement : public Statement {
  public:
   /// Constructor
+  UnlessStatement();
+  /// Constructor
   /// @param condition the condition expression
   /// @param body the body statements
   UnlessStatement(std::unique_ptr<Expression> condition,
diff --git a/src/ast/unless_statement_test.cc b/src/ast/unless_statement_test.cc
new file mode 100644
index 0000000..d4f644f
--- /dev/null
+++ b/src/ast/unless_statement_test.cc
@@ -0,0 +1,124 @@
+// 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 "src/ast/unless_statement.h"
+
+#include "gtest/gtest.h"
+#include "src/ast/identifier_expression.h"
+#include "src/ast/if_statement.h"
+#include "src/ast/nop_statement.h"
+
+namespace tint {
+namespace ast {
+
+using UnlessStatementTest = testing::Test;
+
+TEST_F(UnlessStatementTest, Creation) {
+  auto ident = std::make_unique<IdentifierExpression>("ident");
+  std::vector<std::unique_ptr<Statement>> body;
+  body.push_back(std::make_unique<NopStatement>());
+
+  auto ident_ptr = ident.get();
+  auto nop_ptr = body[0].get();
+
+  UnlessStatement u(std::move(ident), std::move(body));
+  EXPECT_EQ(u.condition(), ident_ptr);
+  ASSERT_EQ(u.body().size(), 1);
+  EXPECT_EQ(u.body()[0].get(), nop_ptr);
+}
+
+TEST_F(UnlessStatementTest, Creation_WithSource) {
+  auto ident = std::make_unique<IdentifierExpression>("ident");
+  std::vector<std::unique_ptr<Statement>> body;
+  body.push_back(std::make_unique<NopStatement>());
+
+  UnlessStatement u(Source{20, 2}, std::move(ident), std::move(body));
+  auto src = u.source();
+  EXPECT_EQ(src.line, 20);
+  EXPECT_EQ(src.column, 2);
+}
+
+TEST_F(UnlessStatementTest, IsUnless) {
+  UnlessStatement stmt;
+  EXPECT_TRUE(stmt.IsUnless());
+}
+
+TEST_F(UnlessStatementTest, IsValid) {
+  auto ident = std::make_unique<IdentifierExpression>("ident");
+  std::vector<std::unique_ptr<Statement>> body;
+  body.push_back(std::make_unique<NopStatement>());
+
+  UnlessStatement u(std::move(ident), std::move(body));
+  EXPECT_TRUE(u.IsValid());
+}
+
+TEST_F(UnlessStatementTest, IsValid_NullCondition) {
+  std::vector<std::unique_ptr<Statement>> body;
+  body.push_back(std::make_unique<NopStatement>());
+
+  UnlessStatement u;
+  u.set_body(std::move(body));
+  EXPECT_FALSE(u.IsValid());
+}
+
+TEST_F(UnlessStatementTest, IsValid_InvalidCondition) {
+  auto ident = std::make_unique<IdentifierExpression>("");
+  std::vector<std::unique_ptr<Statement>> body;
+  body.push_back(std::make_unique<NopStatement>());
+
+  UnlessStatement u(std::move(ident), std::move(body));
+  EXPECT_FALSE(u.IsValid());
+}
+
+TEST_F(UnlessStatementTest, IsValid_NullBodyStatement) {
+  auto ident = std::make_unique<IdentifierExpression>("ident");
+  std::vector<std::unique_ptr<Statement>> body;
+  body.push_back(std::make_unique<NopStatement>());
+  body.push_back(nullptr);
+
+  UnlessStatement u(std::move(ident), std::move(body));
+  EXPECT_FALSE(u.IsValid());
+}
+
+TEST_F(UnlessStatementTest, IsValid_InvalidBodyStatement) {
+  auto ident = std::make_unique<IdentifierExpression>("ident");
+  std::vector<std::unique_ptr<Statement>> body;
+  body.push_back(std::make_unique<NopStatement>());
+  body.push_back(std::make_unique<IfStatement>());
+
+  UnlessStatement u(std::move(ident), std::move(body));
+  EXPECT_FALSE(u.IsValid());
+}
+
+TEST_F(UnlessStatementTest, ToStr) {
+  auto ident = std::make_unique<IdentifierExpression>("ident");
+  std::vector<std::unique_ptr<Statement>> body;
+  body.push_back(std::make_unique<NopStatement>());
+
+  UnlessStatement u(std::move(ident), std::move(body));
+  std::ostringstream out;
+  u.to_str(out, 2);
+  EXPECT_EQ(out.str(), R"(  Unless{
+    (
+      Identifier{ident}
+    )
+    {
+      Nop{}
+    }
+  }
+)");
+}
+
+}  // namespace ast
+}  // namespace tint