diff --git a/libswscale/swscale_unscaled.c b/libswscale/swscale_unscaled.c
index 754edaf0e8..52951e0b43 100644
--- a/libswscale/swscale_unscaled.c
+++ b/libswscale/swscale_unscaled.c
@@ -595,6 +595,9 @@ static rgbConvFn findRgbConvFn(SwsContext *c)
         }
     }
 
+    if ((dstFormat == PIX_FMT_RGB32_1 || dstFormat == PIX_FMT_BGR32_1) && !isRGBA32(srcFormat) && ALT32_CORR<0)
+        return NULL;
+
     return conv;
 }