diff --git a/libavcodec/celp_filters.c b/libavcodec/celp_filters.c
index 6d235184dd..cd475533a5 100644
--- a/libavcodec/celp_filters.c
+++ b/libavcodec/celp_filters.c
@@ -110,6 +110,6 @@ void ff_celp_lp_zero_synthesis_filterf(float *out,
     for (n = 0; n < buffer_length; n++) {
         out[n] = in[n];
         for (i = 1; i < filter_length; i++)
-            out[n] -= filter_coeffs[i-1] * in[n-i];
+            out[n] += filter_coeffs[i-1] * in[n-i];
     }
 }