diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 505ae0af85..410a14ed95 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -3655,6 +3655,40 @@ eval_const_expressions_mutator(Node *node,
 													  context);
 			}
 			break;
+		case T_Var:
+			if (context->root && context->root->parse->rtable)
+			{
+				Var		   *var;
+				Query	   *query;
+				RangeTblEntry *pointedNode;
+
+				var = (Var *)node;
+				query = context->root->parse;
+
+				if (var->varlevelsup != 0)
+					break;
+
+				pointedNode = list_nth(query->rtable, var->varno - 1);
+				Assert(IsA(pointedNode, RangeTblEntry));
+
+				if (pointedNode->rtekind == RTE_FUNCTION && pointedNode->functions->length == 1)
+				{
+					Node	   *result;
+					RangeTblFunction *tblFunction = pointedNode->functions->head->data.ptr_value;
+
+					Assert(IsA(tblFunction, RangeTblFunction));
+					result = eval_const_expressions(context->root, tblFunction->funcexpr);
+
+					if (result->type == T_FuncExpr)
+					{
+						pfree(result);
+						return node;
+					}
+
+					return result;
+				}
+			}
+			break;
 		default:
 			break;
 	}
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index cbc882d47b..eb92f556d8 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -3021,23 +3021,23 @@ select * from
   int4(sin(1)) q1,
   int4(sin(0)) q2
 where q1 = thousand or q2 = thousand;
-                               QUERY PLAN                               
-------------------------------------------------------------------------
- Hash Join
-   Hash Cond: (tenk1.twothousand = int4_tbl.f1)
+                               QUERY PLAN                                
+-------------------------------------------------------------------------
+ Nested Loop
    ->  Nested Loop
-         ->  Nested Loop
-               ->  Function Scan on q1
-               ->  Function Scan on q2
-         ->  Bitmap Heap Scan on tenk1
-               Recheck Cond: ((q1.q1 = thousand) OR (q2.q2 = thousand))
-               ->  BitmapOr
-                     ->  Bitmap Index Scan on tenk1_thous_tenthous
-                           Index Cond: (q1.q1 = thousand)
-                     ->  Bitmap Index Scan on tenk1_thous_tenthous
-                           Index Cond: (q2.q2 = thousand)
-   ->  Hash
-         ->  Seq Scan on int4_tbl
+         ->  Hash Join
+               Hash Cond: (tenk1.twothousand = int4_tbl.f1)
+               ->  Bitmap Heap Scan on tenk1
+                     Recheck Cond: ((1 = thousand) OR (0 = thousand))
+                     ->  BitmapOr
+                           ->  Bitmap Index Scan on tenk1_thous_tenthous
+                                 Index Cond: (1 = thousand)
+                           ->  Bitmap Index Scan on tenk1_thous_tenthous
+                                 Index Cond: (0 = thousand)
+               ->  Hash
+                     ->  Seq Scan on int4_tbl
+         ->  Function Scan on q1
+   ->  Function Scan on q2
 (15 rows)
 
 explain (costs off)
@@ -3046,20 +3046,20 @@ select * from
   int4(sin(1)) q1,
   int4(sin(0)) q2
 where thousand = (q1 + q2);
-                          QUERY PLAN                          
---------------------------------------------------------------
- Hash Join
-   Hash Cond: (tenk1.twothousand = int4_tbl.f1)
+                            QUERY PLAN                             
+-------------------------------------------------------------------
+ Nested Loop
    ->  Nested Loop
-         ->  Nested Loop
-               ->  Function Scan on q1
-               ->  Function Scan on q2
-         ->  Bitmap Heap Scan on tenk1
-               Recheck Cond: (thousand = (q1.q1 + q2.q2))
-               ->  Bitmap Index Scan on tenk1_thous_tenthous
-                     Index Cond: (thousand = (q1.q1 + q2.q2))
-   ->  Hash
-         ->  Seq Scan on int4_tbl
+         ->  Hash Join
+               Hash Cond: (tenk1.twothousand = int4_tbl.f1)
+               ->  Bitmap Heap Scan on tenk1
+                     Recheck Cond: (thousand = 1)
+                     ->  Bitmap Index Scan on tenk1_thous_tenthous
+                           Index Cond: (thousand = 1)
+               ->  Hash
+                     ->  Seq Scan on int4_tbl
+         ->  Function Scan on q1
+   ->  Function Scan on q2
 (12 rows)
 
 --
diff --git a/src/test/regress/expected/rangefuncs.out b/src/test/regress/expected/rangefuncs.out
index 34ca0ef890..973242c33c 100644
--- a/src/test/regress/expected/rangefuncs.out
+++ b/src/test/regress/expected/rangefuncs.out
@@ -1978,7 +1978,7 @@ select x from int8_tbl, extractq2(int8_tbl) f(x);
                 QUERY PLAN                
 ------------------------------------------
  Nested Loop
-   Output: f.x
+   Output: int8_tbl.q2
    ->  Seq Scan on public.int8_tbl
          Output: int8_tbl.q1, int8_tbl.q2
    ->  Function Scan on f