diff --git a/libavcodec/cpia.c b/libavcodec/cpia.c
index bf09e1a5db..81efd70ea1 100644
--- a/libavcodec/cpia.c
+++ b/libavcodec/cpia.c
@@ -111,6 +111,7 @@ static int cpia_decode_frame(AVCodecContext *avctx,
         // Read line length, two byte little endian
         linelength = AV_RL16(src);
         src += 2;
+        src_size -= 2;
 
         if (src_size < linelength) {
             frame->decode_error_flags = FF_DECODE_ERROR_INVALID_BITSTREAM;