diff --git a/src/cmd/compile/internal/types2/builtins.go b/src/cmd/compile/internal/types2/builtins.go
index 808d39fd24..59d2e76ec2 100644
--- a/src/cmd/compile/internal/types2/builtins.go
+++ b/src/cmd/compile/internal/types2/builtins.go
@@ -641,7 +641,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 		if nargs > 0 {
 			params = make([]Type, nargs)
 			for i, a := range args {
-				check.assignment(a, nil, "argument to built-in"+predeclaredFuncs[id].name)
+				check.assignment(a, nil, "argument to built-in "+predeclaredFuncs[id].name)
 				if a.mode == invalid {
 					return
 				}
diff --git a/src/go/types/builtins.go b/src/go/types/builtins.go
index d92a4279f8..2cd6c52b7b 100644
--- a/src/go/types/builtins.go
+++ b/src/go/types/builtins.go
@@ -644,7 +644,7 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 		if nargs > 0 {
 			params = make([]Type, nargs)
 			for i, a := range args {
-				check.assignment(a, nil, "argument to built-in"+predeclaredFuncs[id].name)
+				check.assignment(a, nil, "argument to built-in "+predeclaredFuncs[id].name)
 				if a.mode == invalid {
 					return
 				}