diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index 5fa9491f9c..23e42aaf26 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -322,7 +322,7 @@ void ff_png_filter_row(PNGDSPContext *dsp, uint8_t *dst, int filter_type,
 static void deloco_ ## NAME(TYPE *dst, int size, int alpha) \
 { \
     int i; \
-    for (i = 0; i < size; i += 3 + alpha) { \
+    for (i = 0; i < size - 2; i += 3 + alpha) { \
         int g = dst [i + 1]; \
         dst[i + 0] += g; \
         dst[i + 2] += g; \