diff --git a/mockgen/parse.go b/mockgen/parse.go
index c46221aa..9975ae10 100644
--- a/mockgen/parse.go
+++ b/mockgen/parse.go
@@ -628,4 +628,4 @@ func packageNameOfDir(srcDir string) (string, error) {
 	return packageImport, nil
 }
 
-var errOutsideGoPath = errors.New("Source directory is outside GOPATH")
+var errOutsideGoPath = errors.New("source directory is outside GOPATH")