diff --git a/lib/Sema/SemaStmt.cpp b/lib/Sema/SemaStmt.cpp
index 2598d04..d22deb2 100644
--- a/lib/Sema/SemaStmt.cpp
+++ b/lib/Sema/SemaStmt.cpp
@@ -2836,6 +2836,7 @@
         TokenBuf.resize(32);
         bool StringInvalid = false;
         Asm += SemaRef.PP.getSpelling(AsmToks[j], TokenBuf, &StringInvalid);
+        assert (!StringInvalid && "Expected valid string!");
         break;
       }
       case tok::identifier: {