diff --git a/runtime/vam/expr/arith.go b/runtime/vam/expr/arith.go
index dead4c81e8..8b5449b06e 100644
--- a/runtime/vam/expr/arith.go
+++ b/runtime/vam/expr/arith.go
@@ -24,7 +24,7 @@ func NewArith(sctx *super.Context, op string, lhs, rhs Evaluator) *Arith {
 }
 
 func (a *Arith) Eval(val vector.Any) vector.Any {
-	return vector.Apply(vector.ApplyRipUnions, a.eval, a.lhs.Eval(val), a.rhs.Eval(val))
+	return vector.Apply(vector.ApplyRipUnions|vector.ApplyRipFusions, a.eval, a.lhs.Eval(val), a.rhs.Eval(val))
 }
 
 func (a *Arith) eval(vecs ...vector.Any) (out vector.Any) {
diff --git a/runtime/ztests/expr/arith-nulls.yaml b/runtime/ztests/expr/arith-nulls.yaml
index ca4f0f6556..8c6d51dd12 100644
--- a/runtime/ztests/expr/arith-nulls.yaml
+++ b/runtime/ztests/expr/arith-nulls.yaml
@@ -5,6 +5,7 @@ input: |
   {a:null,b:1}
   {a:null,b:null}
   {a:null::(int64|null),b:2::(int64|null)}
+  {a:fusion(null::(int64|null),<null>),b:fusion(2::(int64|null),<int64>)}
 
 output: |
   null
@@ -27,3 +28,8 @@ output: |
   null
   null
   null
+  null
+  null
+  null
+  null
+  null