diff --git a/libavfilter/asrc_aevalsrc.c b/libavfilter/asrc_aevalsrc.c
index 4c1bbdf1f8..41ad632145 100644
--- a/libavfilter/asrc_aevalsrc.c
+++ b/libavfilter/asrc_aevalsrc.c
@@ -101,6 +101,7 @@ static av_cold int init(AVFilterContext *ctx)
             ret = AVERROR(ENOMEM);
             goto end;
         }
+        eval->expr[eval->nb_channels-1] = NULL;
         ret = av_expr_parse(&eval->expr[eval->nb_channels - 1], expr, var_names,
                             NULL, NULL, NULL, NULL, 0, ctx);
         if (ret < 0)