diff --git a/src/resolver/function_validation_test.cc b/src/resolver/function_validation_test.cc
index 11b704ca18..4cbd7ae8ea 100644
--- a/src/resolver/function_validation_test.cc
+++ b/src/resolver/function_validation_test.cc
@@ -42,7 +42,8 @@ TEST_F(ResolverFunctionValidationTest, FunctionNamesMustBeUnique_fail) {
 
   EXPECT_FALSE(r()->Resolve());
   EXPECT_EQ(r()->error(),
-            "12:34 error v-0016: function names must be unique 'func'");
+            R"(12:34 error v-0016: duplicate function named 'func'
+note: first function declared here)");
 }
 
 TEST_F(ResolverFunctionValidationTest,
diff --git a/src/resolver/resolver.cc b/src/resolver/resolver.cc
index 539e97ec60..5a4d48e231 100644
--- a/src/resolver/resolver.cc
+++ b/src/resolver/resolver.cc
@@ -836,12 +836,15 @@ bool Resolver::ValidateParameter(const VariableInfo* info) {
 
 bool Resolver::ValidateFunction(const ast::Function* func,
                                 const FunctionInfo* info) {
-  if (symbol_to_function_.find(func->symbol()) != symbol_to_function_.end()) {
+  auto func_it = symbol_to_function_.find(func->symbol());
+  if (func_it != symbol_to_function_.end()) {
     diagnostics_.add_error("v-0016",
-                           "function names must be unique '" +
+                           "duplicate function named '" +
                                builder_->Symbols().NameFor(func->symbol()) +
                                "'",
                            func->source());
+    diagnostics_.add_note("first function declared here",
+                          func_it->second->declaration->source());
     return false;
   }