diff --git a/libswscale/swscale_internal.h b/libswscale/swscale_internal.h
index cf157428b3..cdf3754d14 100644
--- a/libswscale/swscale_internal.h
+++ b/libswscale/swscale_internal.h
@@ -273,6 +273,13 @@ const char *sws_format_name(int format);
         || (x)==PIX_FMT_MONOBLACK   \
         || (x)==PIX_FMT_MONOWHITE   \
     )
+#define isALPHA(x)      (           \
+           (x)==PIX_FMT_BGR32       \
+        || (x)==PIX_FMT_BGR32_1     \
+        || (x)==PIX_FMT_RGB32       \
+        || (x)==PIX_FMT_RGB32_1     \
+        || (x)==PIX_FMT_YUVA420P    \
+    )
 
 static inline int fmt_depth(int fmt)
 {