diff --git a/libavcodec/mpegaudiodec.c b/libavcodec/mpegaudiodec.c
index 6c088626fc..d82432c775 100644
--- a/libavcodec/mpegaudiodec.c
+++ b/libavcodec/mpegaudiodec.c
@@ -40,6 +40,7 @@
 
 #define BACKSTEP_SIZE 512
 #define EXTRABYTES 24
+#define LAST_BUF_SIZE 2 * BACKSTEP_SIZE + EXTRABYTES
 
 /* layer 3 "granule" */
 typedef struct GranuleDef {
@@ -63,7 +64,7 @@ typedef struct GranuleDef {
 
 typedef struct MPADecodeContext {
     MPA_DECODE_HEADER
-    uint8_t last_buf[2 * BACKSTEP_SIZE + EXTRABYTES];
+    uint8_t last_buf[LAST_BUF_SIZE];
     int last_buf_size;
     /* next header (used in free format parsing) */
     uint32_t free_format_next_header;
@@ -1378,7 +1379,8 @@ static int mp_decode_layer3(MPADecodeContext *s)
     if (!s->adu_mode) {
         int skip;
         const uint8_t *ptr = s->gb.buffer + (get_bits_count(&s->gb)>>3);
-        int extrasize = av_clip(get_bits_left(&s->gb) >> 3, 0, EXTRABYTES);
+        int extrasize = av_clip(get_bits_left(&s->gb) >> 3, 0,
+                                FFMAX(0, LAST_BUF_SIZE - s->last_buf_size));
         assert((get_bits_count(&s->gb) & 7) == 0);
         /* now we get bits from the main_data_begin offset */
         av_dlog(s->avctx, "seekback: %d\n", main_data_begin);