diff --git a/libavfilter/avf_showcwt.c b/libavfilter/avf_showcwt.c
index 51a45ef636..ee0d697e1e 100644
--- a/libavfilter/avf_showcwt.c
+++ b/libavfilter/avf_showcwt.c
@@ -662,7 +662,7 @@ static void compute_kernel(AVFilterContext *ctx)
 
         for (int n = 0; n < size; n++) {
             if (kernel[size - n - 1].re != 0.f) {
-                kernel_stop[y] = size - n;
+                kernel_stop[y] = size - n - 1;
                 break;
             }
         }