diff --git a/mfbt/tests/TestUtf8.cpp b/mfbt/tests/TestUtf8.cpp
index 03236abf0a60..29654c037fd3 100644
--- a/mfbt/tests/TestUtf8.cpp
+++ b/mfbt/tests/TestUtf8.cpp
@@ -21,7 +21,7 @@ using mozilla::IsValidUtf8;
 using mozilla::Utf8Unit;
 
 // Disable the C++ 2a warning. See bug #1509926
-#if defined(__clang__)
+#if defined(__clang__) && (__clang_major__ >= 6)
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wc++2a-compat"
 #endif
@@ -742,6 +742,6 @@ int main() {
   return 0;
 }
 
-#if defined(__clang__)
+#if defined(__clang__) && (__clang_major__ >= 6)
 #pragma clang diagnostic pop
 #endif
diff --git a/xpcom/tests/gtest/TestStrings.cpp b/xpcom/tests/gtest/TestStrings.cpp
index bf23a6fa640c..ea49dd3cb6f2 100644
--- a/xpcom/tests/gtest/TestStrings.cpp
+++ b/xpcom/tests/gtest/TestStrings.cpp
@@ -30,7 +30,7 @@
   });
 
 // Disable the C++ 2a warning. See bug #1509926
-#if defined(__clang__)
+#if defined(__clang__) && (__clang_major__ >= 6)
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wc++2a-compat"
 #endif
@@ -2345,6 +2345,6 @@ CONVERSION_BENCH(PerfUTF8toUTF16VIThousand, CopyUTF8toUTF16, mViThousandUtf8,
 
 }  // namespace TestStrings
 
-#if defined(__clang__)
+#if defined(__clang__) && (__clang_major__ >= 6)
 #pragma clang diagnostic pop
 #endif