diff --git a/libavfilter/avf_showfreqs.c b/libavfilter/avf_showfreqs.c
index a1ef0bf816..cbbf040c79 100644
--- a/libavfilter/avf_showfreqs.c
+++ b/libavfilter/avf_showfreqs.c
@@ -208,7 +208,7 @@ static void generate_window_func(float *lut, int N, int win_func, float *overlap
         break;
     case WFUNC_BHANN:
         for (n = 0; n < N; n++)
-            lut[n] = 0.62-0.48*FFABS(n/(N-1)-.5)-0.38*cos(2*M_PI*n/(N-1));
+            lut[n] = 0.62-0.48*FFABS(n/(double)(N-1)-.5)-0.38*cos(2*M_PI*n/(N-1));
         *overlap = 0.5;
         break;
     case WFUNC_SINE: