diff --git a/clang/lib/Basic/VirtualFileSystem.cpp b/clang/lib/Basic/VirtualFileSystem.cpp
index f5db717..47c7fa4 100644
--- a/clang/lib/Basic/VirtualFileSystem.cpp
+++ b/clang/lib/Basic/VirtualFileSystem.cpp
@@ -59,6 +59,7 @@
 }
 
 bool Status::equivalent(const Status &Other) const {
+  assert(isStatusKnown() && Other.isStatusKnown());
   return getUniqueID() == Other.getUniqueID();
 }
 bool Status::isDirectory() const {