@@ -170,16 +170,21 @@ static void eval_expr(AVFilterContext *ctx, enum EvalTarget eval_tgt)

 static int set_expr(AVExpr **pexpr, const char *expr, void *log_ctx)

 {

     int ret;

+    AVExpr *old = NULL;

     if (*pexpr)

-        av_expr_free(*pexpr);

-    *pexpr = NULL;

+        old = *pexpr;

     ret = av_expr_parse(pexpr, expr, var_names,

                         NULL, NULL, NULL, NULL, 0, log_ctx);

-    if (ret < 0)

+    if (ret < 0) {

         av_log(log_ctx, AV_LOG_ERROR,

                "Error when evaluating the expression '%s'\n", expr);

-    return ret;

+        *pexpr = old;

+        return ret;

+    }

+

+    av_expr_free(old);

+    return 0;

 }

 static int process_command(AVFilterContext *ctx, const char *cmd, const char *args,