diff --git a/build/clang-plugin/CustomMatchers.h b/build/clang-plugin/CustomMatchers.h
index 54bb0d02dd2e..5a4f8474ec2f 100644
--- a/build/clang-plugin/CustomMatchers.h
+++ b/build/clang-plugin/CustomMatchers.h
@@ -142,6 +142,18 @@ AST_MATCHER(CallExpr, isInWhitelistForFopenUsage) {
   return llvm::sys::path::rbegin(FileName)->equals(Whitelist);
 }
 
+// This matcher will match any node in "gtest-port.h". This file is third-party
+// code (and thus exempt from our rules prohibiting <ctypes.h>), but it's
+// linked into $OBJDIR, so inThirdPartyPath() misclassifies it.
+AST_MATCHER(Stmt, isAllowedToUseLocaleSpecificFunctions) {
+  static const char AllowedFile[] = "gtest-port.h";
+  SourceLocation Loc = Node.getBeginLoc();
+  StringRef FileName =
+      getFilename(Finder->getASTContext().getSourceManager(), Loc);
+
+  return llvm::sys::path::rbegin(FileName)->equals(AllowedFile);
+}
+
 /// This matcher will match a list of files.  These files contain
 /// known NaN-testing expressions which we would like to whitelist.
 AST_MATCHER(BinaryOperator, isInWhitelistForNaNExpr) {
diff --git a/build/clang-plugin/NoLocaleSpecificChecker.cpp b/build/clang-plugin/NoLocaleSpecificChecker.cpp
index 06d534f9ca55..a3543602eb22 100644
--- a/build/clang-plugin/NoLocaleSpecificChecker.cpp
+++ b/build/clang-plugin/NoLocaleSpecificChecker.cpp
@@ -57,11 +57,9 @@ void NoLocaleSpecificChecker::registerMatchers(MatchFinder *AstMatcher) {
                             hasConstCharPtrParam(1),
                             hasIntegerParam(2)),
                       hasNameAndIntegerParam("tolower"),
-                      hasNameAndIntegerParam("toupper")
-                  )
-              )))
-          )
-      ).bind("id"),
+                      hasNameAndIntegerParam("toupper"))))),
+              unless(isAllowedToUseLocaleSpecificFunctions())))
+      .bind("id"),
       this);
 }