diff --git a/runtime/sam/expr/agg/fuser.go b/runtime/sam/expr/agg/fuser.go
index 873ada9ba..cbc29b1af 100644
--- a/runtime/sam/expr/agg/fuser.go
+++ b/runtime/sam/expr/agg/fuser.go
@@ -132,8 +132,8 @@ func (f *Fuser) fuseMono(typ super.Type) super.Type {
 	switch typ := typ.(type) {
 	case *super.TypeRecord:
 		fields := slices.Clone(typ.Fields)
-		for _, field := range fields {
-			field.Type = f.fuseMono(field.Type)
+		for i, field := range fields {
+			fields[i].Type = f.fuseMono(field.Type)
 		}
 		out = f.sctx.MustLookupTypeRecord(fields)
 	case *super.TypeArray:
diff --git a/runtime/ztests/op/aggregate/fuse.yaml b/runtime/ztests/op/aggregate/fuse.yaml
index bf3bad299..0ac3f0e31 100644
--- a/runtime/ztests/op/aggregate/fuse.yaml
+++ b/runtime/ztests/op/aggregate/fuse.yaml
@@ -28,3 +28,17 @@ input: |
 
 output: |
   <{fixed:{x:int64},var:fusion({s:string,a?:[int64],t?:fusion(int64|{x:int64})})}>
+
+---
+
+spq: fuse(this)
+
+vector: true
+
+input: |
+  {a:[1,2]}
+  {a:["foo"]}
+  {a:[null]}
+
+output: |
+  <{a:fusion([fusion(int64|string|null)])}>
diff --git a/runtime/ztests/op/blend.yaml b/runtime/ztests/op/blend.yaml
index b83200521..5997a4591 100644
--- a/runtime/ztests/op/blend.yaml
+++ b/runtime/ztests/op/blend.yaml
@@ -109,6 +109,22 @@ spq: blend
 
 vector: true
 
+input: |
+  {a:[1,2]}
+  {a:["foo"]}
+  {a:[null]}
+
+output: |
+  {a:[1,2]::[int64|string|null]}
+  {a:["foo"]::[int64|string|null]}
+  {a:[null]::[int64|string|null]}
+
+---
+
+spq: blend
+
+vector: true
+
 input: |
   1::=p1
   {a:1::=r1}::=r2
diff --git a/runtime/ztests/op/fuse.yaml b/runtime/ztests/op/fuse.yaml
index 573dcc8d4..e579abde8 100644
--- a/runtime/ztests/op/fuse.yaml
+++ b/runtime/ztests/op/fuse.yaml
@@ -109,6 +109,22 @@ spq: fuse
 
 vector: true
 
+input: |
+  {a:[1,2]}
+  {a:["foo"]}
+  {a:[null]}
+
+output: |
+  {a:fusion([fusion(1::(int64|string|null),<int64>),fusion(2::(int64|string|null),<int64>)],<[int64]>)}
+  {a:fusion([fusion("foo"::(int64|string|null),<string>)],<[string]>)}
+  {a:fusion([fusion(null::(int64|string|null),<null>)],<[null]>)}
+
+---
+
+spq: fuse
+
+vector: true
+
 input: |
   1::=p1
   {a:1::=r1}::=r2