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-rw-r--r--libavcodec/png.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/libavcodec/png.c b/libavcodec/png.c
index 0dd9eaec23..6d588c35a8 100644
--- a/libavcodec/png.c
+++ b/libavcodec/png.c
@@ -850,7 +850,7 @@ static int encode_frame(AVCodecContext *avctx, unsigned char *buf, int buf_size,
for(i = 0; i < 256; i++) {
v = palette[i];
alpha = v >> 24;
- if (alpha != 0xff)
+ if (alpha && alpha != 0xff)
has_alpha = 1;
*alpha_ptr++ = alpha;
ptr[0] = v >> 16;