diff --git a/src/ast/set_decoration_test.cc b/src/ast/set_decoration_test.cc
index 8295e1f630..b257453eb4 100644
--- a/src/ast/set_decoration_test.cc
+++ b/src/ast/set_decoration_test.cc
@@ -34,5 +34,13 @@ TEST_F(SetDecorationTest, Is) {
   EXPECT_TRUE(d.IsSet());
 }
 
+TEST_F(SetDecorationTest, ToStr) {
+  SetDecoration d{2};
+  std::ostringstream out;
+  d.to_str(out);
+  EXPECT_EQ(out.str(), R"(SetDecoration{2}
+)");
+}
+
 }  // namespace ast
 }  // namespace tint