*** a/src/backend/commands/tablecmds.c
--- b/src/backend/commands/tablecmds.c
***************
*** 6734,6739 **** ATExecDropConstraint(Relation rel, const char *constrName,
--- 6734,6740 ----
  	{
  		Oid			childrelid = lfirst_oid(child);
  		Relation	childrel;
+ 		bool		updated = false;
  
  		/* find_inheritance_children already got lock */
  		childrel = heap_open(childrelid, NoLock);
***************
*** 6790,6798 **** ATExecDropConstraint(Relation rel, const char *constrName,
  					con->coninhcount--;
  					simple_heap_update(conrel, &copy_tuple->t_self, copy_tuple);
  					CatalogUpdateIndexes(conrel, copy_tuple);
! 
! 					/* Make update visible */
! 					CommandCounterIncrement();
  				}
  			}
  			else
--- 6791,6798 ----
  					con->coninhcount--;
  					simple_heap_update(conrel, &copy_tuple->t_self, copy_tuple);
  					CatalogUpdateIndexes(conrel, copy_tuple);
! 					/* need to call CommandCounterIncrement() */
! 					updated = true;
  				}
  			}
  			else
***************
*** 6807,6815 **** ATExecDropConstraint(Relation rel, const char *constrName,
  
  				simple_heap_update(conrel, &copy_tuple->t_self, copy_tuple);
  				CatalogUpdateIndexes(conrel, copy_tuple);
! 
! 				/* Make update visible */
! 				CommandCounterIncrement();
  			}
  
  			heap_freetuple(copy_tuple);
--- 6807,6814 ----
  
  				simple_heap_update(conrel, &copy_tuple->t_self, copy_tuple);
  				CatalogUpdateIndexes(conrel, copy_tuple);
! 				/* need to call CommandCounterIncrement() */
! 				updated = true;
  			}
  
  			heap_freetuple(copy_tuple);
***************
*** 6824,6829 **** ATExecDropConstraint(Relation rel, const char *constrName,
--- 6823,6832 ----
  					   constrName,
  					   RelationGetRelationName(childrel))));
  
+ 		/* Make update visible */
+ 		if (updated)
+ 			CommandCounterIncrement();
+ 
  		heap_close(childrel, NoLock);
  	}
  
*** a/src/test/regress/expected/alter_table.out
--- b/src/test/regress/expected/alter_table.out
***************
*** 2103,2105 **** ALTER TABLE tt7 NOT OF;
--- 2103,2112 ----
   x      | integer      | 
   y      | numeric(8,2) | 
  
+ -- make sure we can drop a constraint on the parent but it remains on the child
+ create table test_drop_constr_parent (c text check (c is not null));
+ create table test_drop_constr_child () inherits (test_drop_constr_parent);
+ alter table only test_drop_constr_parent drop constraint "test_drop_constr_parent_c_check";
+ -- should fail
+ insert into test_drop_constr_child (c) values (NULL);
+ ERROR:  new row for relation "test_drop_constr_child" violates check constraint "test_drop_constr_parent_c_check"
*** a/src/test/regress/sql/alter_table.sql
--- b/src/test/regress/sql/alter_table.sql
***************
*** 1456,1458 **** CREATE TYPE tt_t1 AS (x int, y numeric(8,2));
--- 1456,1465 ----
  ALTER TABLE tt7 OF tt_t1;			-- reassign an already-typed table
  ALTER TABLE tt7 NOT OF;
  \d tt7
+ 
+ -- make sure we can drop a constraint on the parent but it remains on the child
+ create table test_drop_constr_parent (c text check (c is not null));
+ create table test_drop_constr_child () inherits (test_drop_constr_parent);
+ alter table only test_drop_constr_parent drop constraint "test_drop_constr_parent_c_check";
+ -- should fail
+ insert into test_drop_constr_child (c) values (NULL);