diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 5f6640c4e87..88f3f9730cc 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -2345,8 +2345,8 @@ 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 3306c696b17..47a7f325901 100644
--- a/src/test/regress/expected/prepare.out
+++ b/src/test/regress/expected/prepare.out
@@ -179,6 +179,17 @@ SELECT name, statement, parameter_types FROM pg_prepared_statements
       |     SELECT * FROM road WHERE thepath = $1;                       | 
 (5 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
@@ -187,3 +198,4 @@ 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 985d0f05c96..006f12f7fb6 100644
--- a/src/test/regress/sql/prepare.sql
+++ b/src/test/regress/sql/prepare.sql
@@ -74,7 +74,22 @@ PREPARE q7(unknown) AS
 SELECT name, statement, parameter_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