diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index a9a09afd2b..93e5658a35 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -4487,8 +4487,8 @@ inline_function(Oid funcid, Oid result_type, Oid result_collid,
 	 * properties.  (The prokind and nargs checks are just paranoia.)
 	 */
 	if (funcform->prolang != SQLlanguageId ||
-		funcform->prosecdef ||
 		funcform->prokind != PROKIND_FUNCTION ||
+		funcform->prosecdef ||
 		funcform->proretset ||
 		funcform->prorettype == RECORDOID ||
 		!heap_attisnull(func_tuple, Anum_pg_proc_proconfig) ||
@@ -4623,9 +4623,18 @@ inline_function(Oid funcid, Oid result_type, Oid result_collid,
 	/* Now we can grab the tlist expression */
 	newexpr = (Node *) ((TargetEntry *) linitial(querytree->targetList))->expr;
 
-	/* Assert that check_sql_fn_retval did the right thing */
-	Assert(exprType(newexpr) == result_type);
-	/* It couldn't have made any dangerous tlist changes, either */
+	/*
+	 * If the SQL function returns VOID, we can only inline it if it is a
+	 * SELECT of an expression returning VOID (ie, it's just a redirection to
+	 * another VOID-returning function).  In all non-VOID-returning cases,
+	 * check_sql_fn_retval should ensure that newexpr returns the function's
+	 * declared result type, so this test shouldn't fail otherwise; but we may
+	 * as well cope gracefully if it does.
+	 */
+	if (exprType(newexpr) != result_type)
+		goto fail;
+
+	/* check_sql_fn_retval couldn't have made any dangerous tlist changes */
 	Assert(!modifyTargetList);
 
 	/*
@@ -5010,12 +5019,16 @@ inline_set_returning_function(PlannerInfo *root, RangeTblEntry *rte)
 	 * properties.  In particular it mustn't be declared STRICT, since we
 	 * couldn't enforce that.  It also mustn't be VOLATILE, because that is
 	 * supposed to cause it to be executed with its own snapshot, rather than
-	 * sharing the snapshot of the calling query.  (Rechecking proretset is
-	 * just paranoia.)
+	 * sharing the snapshot of the calling query.  We also disallow returning
+	 * SETOF VOID, because inlining would result in exposing the actual result
+	 * of the function's last SELECT, which should not happen in that case.
+	 * (Rechecking prokind and proretset is just paranoia.)
 	 */
 	if (funcform->prolang != SQLlanguageId ||
+		funcform->prokind != PROKIND_FUNCTION ||
 		funcform->proisstrict ||
 		funcform->provolatile == PROVOLATILE_VOLATILE ||
+		funcform->prorettype == VOIDOID ||
 		funcform->prosecdef ||
 		!funcform->proretset ||
 		!heap_attisnull(func_tuple, Anum_pg_proc_proconfig))
diff --git a/src/test/regress/expected/create_function_3.out b/src/test/regress/expected/create_function_3.out
index 175f3b59a3..3301885fc8 100644
--- a/src/test/regress/expected/create_function_3.out
+++ b/src/test/regress/expected/create_function_3.out
@@ -1,13 +1,17 @@
 --
 -- CREATE FUNCTION
 --
--- sanity check of pg_proc catalog to the given parameters
+-- Assorted tests using SQL-language functions
 --
+-- All objects made in this test are in temp_func_test schema
 CREATE USER regress_unpriv_user;
 CREATE SCHEMA temp_func_test;
 GRANT ALL ON SCHEMA temp_func_test TO public;
 SET search_path TO temp_func_test, public;
 --
+-- Make sanity checks on the pg_proc entries created by CREATE FUNCTION
+--
+--
 -- ARGUMENT and RETURN TYPES
 --
 CREATE FUNCTION functest_A_1(text, date) RETURNS bool LANGUAGE 'sql'
@@ -127,7 +131,7 @@ SELECT proname, proleakproof FROM pg_proc
  functest_e_2 | t
 (2 rows)
 
-ALTER FUNCTION functest_E_2(int) NOT LEAKPROOF;	-- remove leakproog attribute
+ALTER FUNCTION functest_E_2(int) NOT LEAKPROOF;	-- remove leakproof attribute
 SELECT proname, proleakproof FROM pg_proc
        WHERE oid in ('functest_E_1'::regproc,
                      'functest_E_2'::regproc) ORDER BY proname;
@@ -137,7 +141,7 @@ SELECT proname, proleakproof FROM pg_proc
  functest_e_2 | f
 (2 rows)
 
--- it takes superuser privilege to turn on leakproof, but not for turn off
+-- it takes superuser privilege to turn on leakproof, but not to turn off
 ALTER FUNCTION functest_E_1(int) OWNER TO regress_unpriv_user;
 ALTER FUNCTION functest_E_2(int) OWNER TO regress_unpriv_user;
 SET SESSION AUTHORIZATION regress_unpriv_user;
@@ -146,7 +150,7 @@ ALTER FUNCTION functest_E_1(int) NOT LEAKPROOF;
 ALTER FUNCTION functest_E_2(int) LEAKPROOF;
 ERROR:  only superuser can define a leakproof function
 CREATE FUNCTION functest_E_3(int) RETURNS bool LANGUAGE 'sql'
-       LEAKPROOF AS 'SELECT $1 < 200';	-- failed
+       LEAKPROOF AS 'SELECT $1 < 200';	-- fail
 ERROR:  only superuser can define a leakproof function
 RESET SESSION AUTHORIZATION;
 --
@@ -280,24 +284,66 @@ CREATE OR REPLACE PROCEDURE functest1(a int) LANGUAGE SQL AS 'SELECT $1';
 ERROR:  cannot change routine kind
 DETAIL:  "functest1" is a function.
 DROP FUNCTION functest1(a int);
--- Cleanups
+-- Check behavior of VOID-returning SQL functions
+CREATE FUNCTION voidtest1(a int) RETURNS VOID LANGUAGE SQL AS
+$$ SELECT a + 1 $$;
+SELECT voidtest1(42);
+ voidtest1 
+-----------
+ 
+(1 row)
+
+CREATE FUNCTION voidtest2(a int, b int) RETURNS VOID LANGUAGE SQL AS
+$$ SELECT voidtest1(a + b) $$;
+SELECT voidtest2(11,22);
+ voidtest2 
+-----------
+ 
+(1 row)
+
+-- currently, we can inline voidtest2 but not voidtest1
+EXPLAIN (verbose, costs off) SELECT voidtest2(11,22);
+       QUERY PLAN        
+-------------------------
+ Result
+   Output: voidtest1(33)
+(2 rows)
+
+CREATE TEMP TABLE sometable(f1 int);
+CREATE FUNCTION voidtest3(a int) RETURNS VOID LANGUAGE SQL AS
+$$ INSERT INTO sometable VALUES(a + 1) $$;
+SELECT voidtest3(17);
+ voidtest3 
+-----------
+ 
+(1 row)
+
+CREATE FUNCTION voidtest4(a int) RETURNS VOID LANGUAGE SQL AS
+$$ INSERT INTO sometable VALUES(a - 1) RETURNING f1 $$;
+SELECT voidtest4(39);
+ voidtest4 
+-----------
+ 
+(1 row)
+
+TABLE sometable;
+ f1 
+----
+ 18
+ 38
+(2 rows)
+
+CREATE FUNCTION voidtest5(a int) RETURNS SETOF VOID LANGUAGE SQL AS
+$$ SELECT generate_series(1, a) $$ STABLE;
+SELECT * FROM voidtest5(3);
+ voidtest5 
+-----------
+(0 rows)
+
+-- Cleanup
+\set VERBOSITY terse \\ -- suppress cascade details
 DROP SCHEMA temp_func_test CASCADE;
-NOTICE:  drop cascades to 16 other objects
-DETAIL:  drop cascades to function functest_a_1(text,date)
-drop cascades to function functest_a_2(text[])
-drop cascades to function functest_a_3()
-drop cascades to function functest_b_2(integer)
-drop cascades to function functest_b_3(integer)
-drop cascades to function functest_b_4(integer)
-drop cascades to function functest_c_1(integer)
-drop cascades to function functest_c_2(integer)
-drop cascades to function functest_c_3(integer)
-drop cascades to function functest_e_1(integer)
-drop cascades to function functest_e_2(integer)
-drop cascades to function functest_f_1(integer)
-drop cascades to function functest_f_2(integer)
-drop cascades to function functest_f_3(integer)
-drop cascades to function functest_f_4(integer)
-drop cascades to function functest_b_2(bigint)
+NOTICE:  drop cascades to 21 other objects
+\set VERBOSITY default
 DROP USER regress_unpriv_user;
 RESET search_path;
diff --git a/src/test/regress/sql/create_function_3.sql b/src/test/regress/sql/create_function_3.sql
index 8f209d55af..24bb900990 100644
--- a/src/test/regress/sql/create_function_3.sql
+++ b/src/test/regress/sql/create_function_3.sql
@@ -1,8 +1,11 @@
 --
 -- CREATE FUNCTION
 --
--- sanity check of pg_proc catalog to the given parameters
+-- Assorted tests using SQL-language functions
 --
+
+-- All objects made in this test are in temp_func_test schema
+
 CREATE USER regress_unpriv_user;
 
 CREATE SCHEMA temp_func_test;
@@ -10,6 +13,10 @@ GRANT ALL ON SCHEMA temp_func_test TO public;
 
 SET search_path TO temp_func_test, public;
 
+--
+-- Make sanity checks on the pg_proc entries created by CREATE FUNCTION
+--
+
 --
 -- ARGUMENT and RETURN TYPES
 --
@@ -88,12 +95,12 @@ SELECT proname, proleakproof FROM pg_proc
        WHERE oid in ('functest_E_1'::regproc,
                      'functest_E_2'::regproc) ORDER BY proname;
 
-ALTER FUNCTION functest_E_2(int) NOT LEAKPROOF;	-- remove leakproog attribute
+ALTER FUNCTION functest_E_2(int) NOT LEAKPROOF;	-- remove leakproof attribute
 SELECT proname, proleakproof FROM pg_proc
        WHERE oid in ('functest_E_1'::regproc,
                      'functest_E_2'::regproc) ORDER BY proname;
 
--- it takes superuser privilege to turn on leakproof, but not for turn off
+-- it takes superuser privilege to turn on leakproof, but not to turn off
 ALTER FUNCTION functest_E_1(int) OWNER TO regress_unpriv_user;
 ALTER FUNCTION functest_E_2(int) OWNER TO regress_unpriv_user;
 
@@ -103,7 +110,7 @@ ALTER FUNCTION functest_E_1(int) NOT LEAKPROOF;
 ALTER FUNCTION functest_E_2(int) LEAKPROOF;
 
 CREATE FUNCTION functest_E_3(int) RETURNS bool LANGUAGE 'sql'
-       LEAKPROOF AS 'SELECT $1 < 200';	-- failed
+       LEAKPROOF AS 'SELECT $1 < 200';	-- fail
 
 RESET SESSION AUTHORIZATION;
 
@@ -183,7 +190,38 @@ CREATE OR REPLACE PROCEDURE functest1(a int) LANGUAGE SQL AS 'SELECT $1';
 DROP FUNCTION functest1(a int);
 
 
--- Cleanups
+-- Check behavior of VOID-returning SQL functions
+
+CREATE FUNCTION voidtest1(a int) RETURNS VOID LANGUAGE SQL AS
+$$ SELECT a + 1 $$;
+SELECT voidtest1(42);
+
+CREATE FUNCTION voidtest2(a int, b int) RETURNS VOID LANGUAGE SQL AS
+$$ SELECT voidtest1(a + b) $$;
+SELECT voidtest2(11,22);
+
+-- currently, we can inline voidtest2 but not voidtest1
+EXPLAIN (verbose, costs off) SELECT voidtest2(11,22);
+
+CREATE TEMP TABLE sometable(f1 int);
+
+CREATE FUNCTION voidtest3(a int) RETURNS VOID LANGUAGE SQL AS
+$$ INSERT INTO sometable VALUES(a + 1) $$;
+SELECT voidtest3(17);
+
+CREATE FUNCTION voidtest4(a int) RETURNS VOID LANGUAGE SQL AS
+$$ INSERT INTO sometable VALUES(a - 1) RETURNING f1 $$;
+SELECT voidtest4(39);
+
+TABLE sometable;
+
+CREATE FUNCTION voidtest5(a int) RETURNS SETOF VOID LANGUAGE SQL AS
+$$ SELECT generate_series(1, a) $$ STABLE;
+SELECT * FROM voidtest5(3);
+
+-- Cleanup
+\set VERBOSITY terse \\ -- suppress cascade details
 DROP SCHEMA temp_func_test CASCADE;
+\set VERBOSITY default
 DROP USER regress_unpriv_user;
 RESET search_path;