diff --git a/src/make.bat b/src/make.bat
index 9b0ab6920a4..fd4ce890eb3 100644
--- a/src/make.bat
+++ b/src/make.bat
@@ -28,6 +28,9 @@ cd src
 if "x%GOROOT_FINAL%"=="x" set GOROOT_FINAL=%GOROOT%
 set DEFGOROOT=-DGOROOT_FINAL="\"%GOROOT_FINAL:\=\\%\""
 
+:: Clean old generated file that will cause problems in the build.
+del /F ".\pkg\runtime\runtime_defs.go"
+
 echo # Building C bootstrap tool.
 echo cmd/dist
 if not exist ..\bin\tool mkdir ..\bin\tool