diff --git a/src/cmd/api/goapi.go b/src/cmd/api/goapi.go
index c3ab9c5bcf9..56ba74a5068 100644
--- a/src/cmd/api/goapi.go
+++ b/src/cmd/api/goapi.go
@@ -380,7 +380,7 @@ func (w *Walker) parseFile(dir, file string) (*ast.File, error) {
 		// Just enough to keep the api checker happy.
 		src := "package runtime; type (" +
 			" maptype struct{}; _type struct{}; alg struct{};" +
-			" mspan struct{}; m struct{}; lock struct{}; slicetype struct{};" +
+			" mspan struct{}; m struct{}; mutex struct{}; slicetype struct{};" +
 			" iface struct{}; eface struct{}; interfacetype struct{}; itab struct{};" +
 			" mcache struct{}; bucket struct{}; sudog struct{}; g struct{};" +
 			" hchan struct{}; chantype struct{}; waitq struct{};" +
diff --git a/src/pkg/runtime/syscall_windows.go b/src/pkg/runtime/syscall_windows.go
index 39d8fed1d41..0592c57e1de 100644
--- a/src/pkg/runtime/syscall_windows.go
+++ b/src/pkg/runtime/syscall_windows.go
@@ -9,7 +9,7 @@ import (
 )
 
 type callbacks struct {
-	lock
+	lock mutex
 	ctxt [cb_max]*wincallbackcontext
 	n    int
 }