diff --git a/tools/llvm-upgrade/UpgradeParser.y b/tools/llvm-upgrade/UpgradeParser.y
index 9d2031dc740..6132eeb558c 100644
--- a/tools/llvm-upgrade/UpgradeParser.y
+++ b/tools/llvm-upgrade/UpgradeParser.y
@@ -18,6 +18,7 @@
 #include <map>
 #include <utility>
 #include <iostream>
+#include <cassert>
 
 #define YYERROR_VERBOSE 1
 #define YYINCLUDED_STDLIB_H