fix corner case in `merge_vars` (#4407)

fixes #4406

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 1249e620..ab68c45d 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -4801,7 +4801,7 @@ merge(Compressor.prototype, {
             if (node instanceof AST_Call) {
                 var exp = node.expression;
                 var tail = exp.tail_node();
-                if (!(tail instanceof AST_Function)) return;
+                if (!is_function(tail)) return;
                 if (exp !== tail) exp.expressions.slice(0, -1).forEach(function(node) {
                     node.walk(tw);
                 });