diff --git a/src/ast/call_expression_test.cc b/src/ast/call_expression_test.cc
index b4dad2f..1425f06 100644
--- a/src/ast/call_expression_test.cc
+++ b/src/ast/call_expression_test.cc
@@ -19,6 +19,7 @@
 
 namespace tint {
 namespace ast {
+namespace {
 
 using CallExpressionTest = testing::Test;
 
@@ -127,5 +128,6 @@
 )");
 }
 
+}  // namespace
 }  // namespace ast
 }  // namespace tint