diff --git a/clang/lib/Tooling/Syntax/BuildTree.cpp b/clang/lib/Tooling/Syntax/BuildTree.cpp
index 21ac6b8bda62db..4e76b3825b6f4c 100644
--- a/clang/lib/Tooling/Syntax/BuildTree.cpp
+++ b/clang/lib/Tooling/Syntax/BuildTree.cpp
@@ -769,6 +769,7 @@ class BuildTreeVisitor : public RecursiveASTVisitor<BuildTreeVisitor> {
       llvm::report_fatal_error("We don't yet support the __super specifier",
                                true);
     }
+    llvm_unreachable("Unhandled NestedNameSpecifier::SpecifierKind enum");
   }
 
   // FIXME: Fix `NestedNameSpecifierLoc::getLocalSourceRange` for the