diff --git a/cc/config/tidy.go b/cc/config/tidy.go
index 8b5289d..ad205cf 100644
--- a/cc/config/tidy.go
+++ b/cc/config/tidy.go
@@ -205,11 +205,18 @@
 	return tidyDefault
 }
 
-func NoClangTidyForDir(dir string) bool {
+func neverTidyForDir(dir string) bool {
+	// This function can be extended if tidy needs to be disabled for more directories.
+	return strings.HasPrefix(dir, "external/grpc-grpc")
+}
+
+func NoClangTidyForDir(allowExternalVendor bool, dir string) bool {
+	// Tidy can be disable for a module in dir, if the dir is "neverTidyForDir",
+	// or if it belongs to external|vendor and !allowExternalVendor.
 	// This function depends on TidyChecksForDir, which selects tidyExternalVendor
-	// checks for external/vendor projects. For those projects we disable clang-tidy
-	// by default, unless some modules enable clang-tidy with tidy:true.
-	return TidyChecksForDir(dir) == tidyExternalVendor
+	// checks for external/vendor projects.
+	return neverTidyForDir(dir) ||
+		(!allowExternalVendor && TidyChecksForDir(dir) == tidyExternalVendor)
 }
 
 // Returns a globally disabled tidy checks, overriding locally selected checks.
diff --git a/cc/tidy.go b/cc/tidy.go
index 2ba13ca..810d089 100644
--- a/cc/tidy.go
+++ b/cc/tidy.go
@@ -79,9 +79,10 @@
 	// Some projects like external/* and vendor/* have clang-tidy disabled by default,
 	// unless they are enabled explicitly with the "tidy:true" property or
 	// when TIDY_EXTERNAL_VENDOR is set to true.
-	if !ctx.Config().IsEnvTrue("TIDY_EXTERNAL_VENDOR") &&
-		!proptools.Bool(tidy.Properties.Tidy) &&
-		config.NoClangTidyForDir(ctx.ModuleDir()) {
+	if !proptools.Bool(tidy.Properties.Tidy) &&
+		config.NoClangTidyForDir(
+			ctx.Config().IsEnvTrue("TIDY_EXTERNAL_VENDOR"),
+			ctx.ModuleDir()) {
 		return flags
 	}
 	// If not explicitly disabled, set flags.Tidy to generate .tidy rules.