diff --git a/libavformat/ffmdec.c b/libavformat/ffmdec.c
index 178d80860c..97cd1292a6 100644
--- a/libavformat/ffmdec.c
+++ b/libavformat/ffmdec.c
@@ -119,7 +119,7 @@ static int ffm_read_data(AVFormatContext *s,
                     return 0;
                 }
                 ffm->first_packet = 0;
-                if ((frame_offset & 0x7ffff) < FFM_HEADER_SIZE)
+                if ((frame_offset & 0x7fff) < FFM_HEADER_SIZE)
                     return -1;
                 ffm->packet_ptr = ffm->packet + (frame_offset & 0x7fff) - FFM_HEADER_SIZE;
                 if (!first)