diff --git a/clang/lib/Format/FormatTokenSource.h b/clang/lib/Format/FormatTokenSource.h
index 8bf7e6932c895..0be46287f6b74 100644
--- a/clang/lib/Format/FormatTokenSource.h
+++ b/clang/lib/Format/FormatTokenSource.h
@@ -236,7 +236,7 @@ class ScopedMacroState : public FormatTokenSource {
   }
 
   FormatToken *insertTokens(ArrayRef<FormatToken *> Tokens) override {
-    assert(false && "Cannot insert tokens while parsing a macro.");
+    llvm_unreachable("Cannot insert tokens while parsing a macro.");
   }
 
 private: