diff --git a/lib/Basic/VirtualFileSystem.cpp b/lib/Basic/VirtualFileSystem.cpp
index f5db717866a9..47c7fa4ba77f 100644
--- a/lib/Basic/VirtualFileSystem.cpp
+++ b/lib/Basic/VirtualFileSystem.cpp
@@ -59,6 +59,7 @@ Status Status::copyWithNewName(const file_status &In, StringRef NewName) {
 }
 
 bool Status::equivalent(const Status &Other) const {
+  assert(isStatusKnown() && Other.isStatusKnown());
   return getUniqueID() == Other.getUniqueID();
 }
 bool Status::isDirectory() const {