Index: lib/CodeGen/CGDebugInfo.cpp
===================================================================
--- lib/CodeGen/CGDebugInfo.cpp
+++ lib/CodeGen/CGDebugInfo.cpp
@@ -2650,6 +2650,7 @@
       SM.getExpansionLoc(CurLoc) == SM.getExpansionLoc(PrevLoc))
     // New Builder may not be in sync with CGDebugInfo.
     if (!Builder.getCurrentDebugLocation().isUnknown() &&
+        LexicalBlockStack.size() &&
         Builder.getCurrentDebugLocation().getScope(CGM.getLLVMContext()) ==
             LexicalBlockStack.back())
       return;
@@ -2657,7 +2658,10 @@
   // Update last state.
   PrevLoc = CurLoc;
 
-  llvm::MDNode *Scope = LexicalBlockStack.back();
+  llvm::MDNode *Scope =
+      LexicalBlockStack.size()
+          ? LexicalBlockStack.back()
+          : Builder.getCurrentDebugLocation().getScope(CGM.getLLVMContext());
   Builder.SetCurrentDebugLocation(llvm::DebugLoc::get(
       getLineNumber(CurLoc), getColumnNumber(CurLoc, ForceColumnInfo), Scope));
 }