diff --git a/runtime/op/join/join.go b/runtime/op/join/join.go
index d4238a93b4..e115d3abd5 100644
--- a/runtime/op/join/join.go
+++ b/runtime/op/join/join.go
@@ -50,13 +50,13 @@ func New(octx *op.Context, anti, inner bool, left, right zbuf.Puller, leftKey, r
 	}
 	// Add sorts if needed.
 	if !leftDir.HasOrder(o) {
-		left, err = sort.New(octx, left, []expr.Evaluator{leftKey}, o, true)
+		left, err = sort.New(octx, left, []expr.Evaluator{leftKey}, o, false)
 		if err != nil {
 			return nil, err
 		}
 	}
 	if !rightDir.HasOrder(o) {
-		right, err = sort.New(octx, right, []expr.Evaluator{rightKey}, o, true)
+		right, err = sort.New(octx, right, []expr.Evaluator{rightKey}, o, false)
 		if err != nil {
 			return nil, err
 		}
diff --git a/runtime/op/join/ztests/auto-sort.yaml b/runtime/op/join/ztests/auto-sort.yaml
index e6a5f76ba3..56c17167e9 100644
--- a/runtime/op/join/ztests/auto-sort.yaml
+++ b/runtime/op/join/ztests/auto-sort.yaml
@@ -14,30 +14,38 @@ script: |
 inputs:
   - name: a.zson
     data: |
+      {a:null(int64)}
       {a:1}
       {a:2}
   - name: b.zson
     data: |
       {b:2}
       {b:1}
+      {b:null(int64)}
 
 outputs:
   - name: stdout
     data: |
       {a:1}
       {a:2}
+      {a:null(int64)}
       // ===
       {a:2}
       {a:1}
+      {a:null(int64)}
       // ===
       {a:1}
       {a:2}
+      {a:null(int64)}
       // ===
       {a:1}
       {a:2}
+      {a:null(int64)}
       // ===
       {a:2}
       {a:1}
+      {a:null(int64)}
       // ===
       {a:2}
       {a:1}
+      {a:null(int64)}