diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 04445166bf3..7d4cd4aa2c7 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -2306,8 +2306,8 @@ transformSetOperationTree(ParseState *pstate, SelectStmt *stmt,
 			if (rcoltype != UNKNOWNOID)
 				rcolnode = coerce_to_common_type(pstate, rcolnode,
 												 rescoltype, context);
-			else if ((IsA(lcolnode, Const) ||
-					 IsA(lcolnode, Param)) && sql_dialect != SQL_DIALECT_TSQL)
+			else if ((IsA(rcolnode, Const) ||
+					 IsA(rcolnode, Param)) && sql_dialect != SQL_DIALECT_TSQL)
 			{
 				rcolnode = coerce_to_common_type(pstate, rcolnode,
 												 rescoltype, context);
diff --git a/src/test/regress/expected/prepare.out b/src/test/regress/expected/prepare.out
index 5815e17b39c..9ba7ffc74fc 100644
--- a/src/test/regress/expected/prepare.out
+++ b/src/test/regress/expected/prepare.out
@@ -184,6 +184,17 @@ SELECT name, statement, parameter_types, result_types FROM pg_prepared_statement
       |     UPDATE tenk1 SET stringu1 = $2 WHERE unique1 = $1;           |                                                    | 
 (6 rows)
 
+CREATE TABLE union_type (id int primary key, name varchar(20));
+PREPARE q9
+AS
+WITH temp1 AS (
+    SELECT * from union_type
+    UNION
+    SELECT
+        $1 AS id,
+        $2 AS name
+)
+SELECT * from temp1;
 -- test DEALLOCATE ALL;
 DEALLOCATE ALL;
 SELECT name, statement, parameter_types FROM pg_prepared_statements
@@ -192,3 +203,4 @@ SELECT name, statement, parameter_types FROM pg_prepared_statements
 ------+-----------+-----------------
 (0 rows)
 
+DROP table union_type;
diff --git a/src/test/regress/sql/prepare.sql b/src/test/regress/sql/prepare.sql
index c6098dc95ce..6d57a8e9266 100644
--- a/src/test/regress/sql/prepare.sql
+++ b/src/test/regress/sql/prepare.sql
@@ -78,7 +78,22 @@ PREPARE q8 AS
 SELECT name, statement, parameter_types, result_types FROM pg_prepared_statements
     ORDER BY name;
 
+CREATE TABLE union_type (id int primary key, name varchar(20));
+
+PREPARE q9
+AS
+WITH temp1 AS (
+    SELECT * from union_type
+    UNION
+    SELECT
+        $1 AS id,
+        $2 AS name
+)
+SELECT * from temp1;
+
 -- test DEALLOCATE ALL;
 DEALLOCATE ALL;
 SELECT name, statement, parameter_types FROM pg_prepared_statements
     ORDER BY name;
+
+DROP table union_type;
\ No newline at end of file