diff --git a/include/llvm/MC/MCAsmLexer.h b/include/llvm/MC/MCAsmLexer.h
index be5083becc4..b1b4dd1155e 100644
--- a/include/llvm/MC/MCAsmLexer.h
+++ b/include/llvm/MC/MCAsmLexer.h
@@ -11,6 +11,7 @@
 #define LLVM_MC_MCASMLEXER_H
 
 #include "llvm/ADT/StringRef.h"
+#include "llvm/Support/DataTypes.h"
 
 namespace llvm {
 class MCAsmLexer;