diff --git a/runtime/expr/agg/collect.go b/runtime/expr/agg/collect.go
index 060148e7ac..6bb88ce316 100644
--- a/runtime/expr/agg/collect.go
+++ b/runtime/expr/agg/collect.go
@@ -22,7 +22,7 @@ func (c *Collect) Consume(val *zed.Value) {
 }
 
 func (c *Collect) update(val *zed.Value) {
-	c.values = append(c.values, *val.Copy())
+	c.values = append(c.values, *val.Under(&zed.Value{}).Copy())
 	c.size += len(val.Bytes())
 	for c.size > MaxValueSize {
 		// XXX See issue #1813.  For now we silently discard entries
diff --git a/runtime/expr/agg/ztests/collect-untag-unions.yaml b/runtime/expr/agg/ztests/collect-untag-unions.yaml
new file mode 100644
index 0000000000..b94ea627fe
--- /dev/null
+++ b/runtime/expr/agg/ztests/collect-untag-unions.yaml
@@ -0,0 +1,9 @@
+zed: collect(this)
+
+input: |
+  1((int64,string))
+  "foo"((time,string))
+  0.5
+
+output: |
+  [1,"foo",0.5]