diff --git a/libavcodec/celp_filters.c b/libavcodec/celp_filters.c
index fafedd99a3..40ff7427df 100644
--- a/libavcodec/celp_filters.c
+++ b/libavcodec/celp_filters.c
@@ -65,11 +65,11 @@ int ff_celp_lp_synthesis_filter(int16_t *out, const int16_t *filter_coeffs,
     int i,n;
 
     for (n = 0; n < buffer_length; n++) {
-        int sum = -rounder, sum1;
+        int sum = rounder, sum1;
         for (i = 1; i <= filter_length; i++)
-            sum += (unsigned)(filter_coeffs[i-1] * out[n-i]);
+            sum -= (unsigned)(filter_coeffs[i-1] * out[n-i]);
 
-        sum1 = ((-sum >> 12) + in[n]) >> shift;
+        sum1 = ((sum >> 12) + in[n]) >> shift;
         sum  = av_clip_int16(sum1);
 
         if (stop_on_overflow && sum != sum1)