diff --git a/clang/lib/Basic/Module.cpp b/clang/lib/Basic/Module.cpp
index baeeb9e..e119c05 100644
--- a/clang/lib/Basic/Module.cpp
+++ b/clang/lib/Basic/Module.cpp
@@ -492,6 +492,7 @@
 
 void VisibleModuleSet::setVisible(Module *M, SourceLocation Loc,
                                   VisibleCallback Vis, ConflictCallback Cb) {
+  assert(Loc.isValid() && "setVisible expects a valid import location");
   if (isVisible(M))
     return;