diff --git a/include/freetype/freetype.h b/include/freetype/freetype.h
index 90e08881b..44d1b1acc 100644
--- a/include/freetype/freetype.h
+++ b/include/freetype/freetype.h
@@ -2593,8 +2593,8 @@ FT_BEGIN_HEADER
    *   stream attachments.
    */
   FT_EXPORT( FT_Error )
-  FT_Attach_Stream( FT_Face        face,
-                    FT_Open_Args*  parameters );
+  FT_Attach_Stream( FT_Face              face,
+                    const FT_Open_Args*  parameters );
 
 
   /**************************************************************************
diff --git a/src/base/ftobjs.c b/src/base/ftobjs.c
index 65945cbeb..7f1f063cc 100644
--- a/src/base/ftobjs.c
+++ b/src/base/ftobjs.c
@@ -2854,8 +2854,8 @@
   /* documentation is in freetype.h */
 
   FT_EXPORT_DEF( FT_Error )
-  FT_Attach_Stream( FT_Face        face,
-                    FT_Open_Args*  parameters )
+  FT_Attach_Stream( FT_Face              face,
+                    const FT_Open_Args*  parameters )
   {
     FT_Stream  stream;
     FT_Error   error;