diff --git a/go/vt/vtgate/planbuilder/operators/union_merging.go b/go/vt/vtgate/planbuilder/operators/union_merging.go
index 1fb7d4fb454..67853e44c7f 100644
--- a/go/vt/vtgate/planbuilder/operators/union_merging.go
+++ b/go/vt/vtgate/planbuilder/operators/union_merging.go
@@ -17,8 +17,6 @@ limitations under the License.
 package operators
 
 import (
-	"vitess.io/vitess/go/mysql/collations"
-	"vitess.io/vitess/go/sqltypes"
 	"vitess.io/vitess/go/vt/sqlparser"
 	"vitess.io/vitess/go/vt/vtgate/engine"
 	"vitess.io/vitess/go/vt/vtgate/evalengine"
@@ -205,10 +203,12 @@ func createMergedUnion(
 		rt, foundR := ctx.SemTable.TypeForExpr(rae.Expr)
 		lt, foundL := ctx.SemTable.TypeForExpr(lae.Expr)
 		if foundR && foundL {
-			types := []sqltypes.Type{rt.Type(), lt.Type()}
-			t := evalengine.AggregateTypes(types)
-			ctx.SemTable.ExprTypes[col] = evalengine.NewType(t, collations.Unknown)
+			t, err := evalengine.AggregateEvalTypes([]evalengine.Type{rt, lt}, ctx.VSchema.Environment().CollationEnv())
+			if err == nil {
+				ctx.SemTable.ExprTypes[col] = t
+			}
 		}
+
 		ctx.SemTable.Recursive[col] = deps
 	}
 
diff --git a/go/vt/vtgate/planbuilder/testdata/postprocess_cases.json b/go/vt/vtgate/planbuilder/testdata/postprocess_cases.json
index 6697da92c23..9093fe2f390 100644
--- a/go/vt/vtgate/planbuilder/testdata/postprocess_cases.json
+++ b/go/vt/vtgate/planbuilder/testdata/postprocess_cases.json
@@ -2205,5 +2205,35 @@
         "user.user"
       ]
     }
+  },
+  {
+    "comment": "No weightstrings or derived table needed",
+    "query": "select textcol1 from user union select textcol1 from user",
+    "plan": {
+      "QueryType": "SELECT",
+      "Original": "select textcol1 from user union select textcol1 from user",
+      "Instructions": {
+        "OperatorType": "Distinct",
+        "Collations": [
+          "0: latin1_swedish_ci"
+        ],
+        "Inputs": [
+          {
+            "OperatorType": "Route",
+            "Variant": "Scatter",
+            "Keyspace": {
+              "Name": "user",
+              "Sharded": true
+            },
+            "FieldQuery": "select textcol1 from `user` where 1 != 1 union select textcol1 from `user` where 1 != 1",
+            "Query": "select textcol1 from `user` union select textcol1 from `user`",
+            "Table": "`user`"
+          }
+        ]
+      },
+      "TablesUsed": [
+        "user.user"
+      ]
+    }
   }
 ]