diff --git a/core/fpdfapi/edit/cpdf_stringarchivestream.h b/core/fpdfapi/edit/cpdf_stringarchivestream.h
index b1b5f72..4107122 100644
--- a/core/fpdfapi/edit/cpdf_stringarchivestream.h
+++ b/core/fpdfapi/edit/cpdf_stringarchivestream.h
@@ -5,6 +5,8 @@
 #ifndef CORE_FPDFAPI_EDIT_CPDF_STRINGARCHIVESTREAM_H_
 #define CORE_FPDFAPI_EDIT_CPDF_STRINGARCHIVESTREAM_H_
 
+#include <iosfwd>
+
 #include "core/fxcrt/fx_stream.h"
 
 class CPDF_StringArchiveStream final : public IFX_ArchiveStream {