diff --git a/libavcodec/acelp_vectors.c b/libavcodec/acelp_vectors.c
index 86851a3a8a..798217d73b 100644
--- a/libavcodec/acelp_vectors.c
+++ b/libavcodec/acelp_vectors.c
@@ -22,6 +22,7 @@
 
 #include <inttypes.h>
 
+#include "libavutil/avassert.h"
 #include "libavutil/common.h"
 #include "libavutil/float_dsp.h"
 #include "avcodec.h"
@@ -240,6 +241,7 @@ void ff_set_fixed_vector(float *out, const AMRFixed *in, float scale, int size)
         float y = in->y[i] * scale;
 
         if (in->pitch_lag > 0)
+            av_assert0(x < size);
             do {
                 out[x] += y;
                 y *= in->pitch_fac;