diff --git a/clang-tools-extra/clang-tidy/misc/UnconventionalAssignOperatorCheck.cpp b/clang-tools-extra/clang-tidy/misc/UnconventionalAssignOperatorCheck.cpp
--- a/clang-tools-extra/clang-tidy/misc/UnconventionalAssignOperatorCheck.cpp
+++ b/clang-tools-extra/clang-tidy/misc/UnconventionalAssignOperatorCheck.cpp
@@ -73,9 +73,14 @@
   if (const auto *RetStmt = Result.Nodes.getNodeAs<ReturnStmt>("returnStmt")) {
     diag(RetStmt->getBeginLoc(), "operator=() should always return '*this'");
   } else {
+    const ASTContext *ASTCtx = Result.Context;
+    const LangOptions &Opts = ASTCtx->getLangOpts();
     static const char *const Messages[][2] = {
         {"ReturnType", "operator=() should return '%0&'"},
-        {"ArgumentType", "operator=() should take '%0 const&', '%0&&' or '%0'"},
+        {"ArgumentType",
+         Opts.CPlusPlus11
+             ? "operator=() should take '%0 const&', '%0&&' or '%0'"
+             : "operator=() should take '%0 const&' or '%0'"},
         {"cv", "operator=() should not be marked '%1'"}};
 
     const auto *Method = Result.Nodes.getNodeAs<CXXMethodDecl>("method");