diff --git a/clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.h b/clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.h
--- a/clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.h
+++ b/clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.h
@@ -59,6 +59,9 @@
     /// automatically.
     ConflictsWithMacroDefinition,
 
+    /// The fixup results in an identifier that is not a valid c/c++ identifier.
+    FixInvalidIdentifier,
+
     /// Values pass this threshold will be ignored completely
     /// i.e no message, no fixup.
     IgnoreFailureThreshold,
diff --git a/clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.cpp b/clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.cpp
--- a/clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.cpp
+++ b/clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.cpp
@@ -10,6 +10,7 @@
 #include "ASTUtils.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Basic/CharInfo.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Lex/PPCallbacks.h"
 #include "clang/Lex/Preprocessor.h"
@@ -463,6 +464,8 @@
         Failure.FixStatus = ShouldFixStatus::ConflictsWithKeyword;
       else if (Ident->hasMacroDefinition())
         Failure.FixStatus = ShouldFixStatus::ConflictsWithMacroDefinition;
+    } else if (!isValidIdentifier(Info.Fixup)) {
+      Failure.FixStatus = ShouldFixStatus::FixInvalidIdentifier;
     }
 
     Failure.Info = std::move(Info);
@@ -517,6 +520,9 @@
       RenamerClangTidyCheck::ShouldFixStatus::ConflictsWithMacroDefinition)
     return "; cannot be fixed because '" + Fixup +
            "' would conflict with a macro definition";
+  if (FixStatus == RenamerClangTidyCheck::ShouldFixStatus::FixInvalidIdentifier)
+    return "; cannot be fixed because '" + Fixup +
+           "' is not a valid identifier";
 
   llvm_unreachable("invalid ShouldFixStatus");
 }
diff --git a/clang-tools-extra/test/clang-tidy/checkers/readability-identifier-naming-bugfix-name-conflicts.cpp b/clang-tools-extra/test/clang-tidy/checkers/readability-identifier-naming-bugfix-name-conflicts.cpp
--- a/clang-tools-extra/test/clang-tidy/checkers/readability-identifier-naming-bugfix-name-conflicts.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/readability-identifier-naming-bugfix-name-conflicts.cpp
@@ -25,3 +25,13 @@
 
   return 0;
 }
+
+int func3(int _0Bad) {
+  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: invalid case style for parameter '_0Bad'; cannot be fixed because '0_bad' is not a valid identifier [readability-identifier-naming]
+  // CHECK-FIXES: {{^}}int func3(int _0Bad) {{{$}}
+  if (_0Bad == 1) {
+    // CHECK-FIXES: {{^}}  if (_0Bad == 1) {{{$}}
+    return 2;
+  }
+  return 0;
+}