diff --git a/clang-tools-extra/include-cleaner/lib/IncludeSpeller.cpp b/clang-tools-extra/include-cleaner/lib/IncludeSpeller.cpp
index 8e6143820a2b7..bb49630fe3c80 100644
--- a/clang-tools-extra/include-cleaner/lib/IncludeSpeller.cpp
+++ b/clang-tools-extra/include-cleaner/lib/IncludeSpeller.cpp
@@ -34,6 +34,7 @@ class DefaultIncludeSpeller : public IncludeSpeller {
           Input.H.physical(), Input.Main->tryGetRealPathName(), &IsSystem);
       return IsSystem ? "<" + FinalSpelling + ">" : "\"" + FinalSpelling + "\"";
     }
+    llvm_unreachable("Unknown clang::include_cleaner::Header::Kind enum");
   }
 };