diff --git a/include/freetype/internal/ftdriver.h b/include/freetype/internal/ftdriver.h
index a981b6df0..89a92ab7e 100644
--- a/include/freetype/internal/ftdriver.h
+++ b/include/freetype/internal/ftdriver.h
@@ -58,7 +58,7 @@ FT_BEGIN_HEADER
 
   typedef FT_Error
   (*FT_Size_SelectFunc)( FT_Size   size,
-                         FT_ULong  index );
+                         FT_ULong  size_index );
 
   typedef FT_Error
   (*FT_Slot_LoadFunc)( FT_GlyphSlot  slot,
diff --git a/include/freetype/internal/ftobjs.h b/include/freetype/internal/ftobjs.h
index 46253c6b0..f07e23d5b 100644
--- a/include/freetype/internal/ftobjs.h
+++ b/include/freetype/internal/ftobjs.h
@@ -479,7 +479,7 @@ FT_BEGIN_HEADER
   FT_Match_Size( FT_Face          face,
                  FT_Size_Request  req,
                  FT_Bool          ignore_width,
-                 FT_ULong*        index );
+                 FT_ULong*        size_index );
 
 
   /* Use the horizontal metrics to synthesize the vertical metrics. */