diff --git a/include/llvm/Assembly/Writer.h b/include/llvm/Assembly/Writer.h
index 34d905399d4..5e5fe156058 100644
--- a/include/llvm/Assembly/Writer.h
+++ b/include/llvm/Assembly/Writer.h
@@ -18,6 +18,7 @@
 #define LLVM_ASSEMBLY_WRITER_H
 
 #include <iosfwd>
+#include <string>
 
 namespace llvm {