diff --git a/tools/llvmc/ConfigLexer.h b/tools/llvmc/ConfigLexer.h
index 7a9693d5b53..f947da2bf2c 100644
--- a/tools/llvmc/ConfigLexer.h
+++ b/tools/llvmc/ConfigLexer.h
@@ -15,6 +15,7 @@
 
 #include <string>
 #include <istream>
+#include <cassert>
 
 namespace llvm {