diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index 784feae..ecadcbd 100644
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -42,7 +42,7 @@ ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
     ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET ( <replaceable class="PARAMETER">attribute_option</replaceable> = <replaceable class="PARAMETER">value</replaceable> [, ... ] )
     ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> RESET ( <replaceable class="PARAMETER">attribute_option</replaceable> [, ... ] )
     ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
-    ADD <replaceable class="PARAMETER">table_constraint</replaceable>
+    ADD <replaceable class="PARAMETER">table_constraint</replaceable> [ ENFORCED | NOT ENFORCED ]
     DROP CONSTRAINT [ IF EXISTS ]  <replaceable class="PARAMETER">constraint_name</replaceable> [ RESTRICT | CASCADE ]
     DISABLE TRIGGER [ <replaceable class="PARAMETER">trigger_name</replaceable> | ALL | USER ]
     ENABLE TRIGGER [ <replaceable class="PARAMETER">trigger_name</replaceable> | ALL | USER ]
@@ -220,11 +220,13 @@ ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
    </varlistentry>
 
    <varlistentry>
-    <term><literal>ADD <replaceable class="PARAMETER">table_constraint</replaceable></literal></term>
+    <term><literal>ADD <replaceable class="PARAMETER">table_constraint</replaceable> [ ENFORCED | NOT ENFORCED ]</literal></term>
     <listitem>
      <para>
       This form adds a new constraint to a table using the same syntax as
-      <xref linkend="SQL-CREATETABLE">.
+      <xref linkend="SQL-CREATETABLE">. Newly added constraints can be defined
+      as <literal>NOT ENFORCED</literal>, rather than the default setting
+      <literal>ENFORCED</literal>.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 937992b..3cacad0 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -304,13 +304,13 @@ static void ATExecAddIndex(AlteredTableInfo *tab, Relation rel,
 			   IndexStmt *stmt, bool is_rebuild, LOCKMODE lockmode);
 static void ATExecAddConstraint(List **wqueue,
 					AlteredTableInfo *tab, Relation rel,
-					Constraint *newConstraint, bool recurse, LOCKMODE lockmode);
+					Constraint *newConstraint, bool recurse, LOCKMODE lockmode, bool enforced);
 static void ATAddCheckConstraint(List **wqueue,
 					 AlteredTableInfo *tab, Relation rel,
 					 Constraint *constr,
 					 bool recurse, bool recursing, LOCKMODE lockmode);
 static void ATAddForeignKeyConstraint(AlteredTableInfo *tab, Relation rel,
-						  Constraint *fkconstraint, LOCKMODE lockmode);
+						  Constraint *fkconstraint, LOCKMODE lockmode, bool enforced);
 static void ATExecDropConstraint(Relation rel, const char *constrName,
 					 DropBehavior behavior,
 					 bool recurse, bool recursing,
@@ -2970,11 +2970,11 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
 			break;
 		case AT_AddConstraint:	/* ADD CONSTRAINT */
 			ATExecAddConstraint(wqueue, tab, rel, (Constraint *) cmd->def,
-								false, lockmode);
+								false, lockmode, cmd->enforced);
 			break;
 		case AT_AddConstraintRecurse:	/* ADD CONSTRAINT with recursion */
 			ATExecAddConstraint(wqueue, tab, rel, (Constraint *) cmd->def,
-								true, lockmode);
+								true, lockmode, cmd->enforced);
 			break;
 		case AT_DropConstraint:	/* DROP CONSTRAINT */
 			ATExecDropConstraint(rel, cmd->name, cmd->behavior,
@@ -4914,7 +4914,7 @@ ATExecAddIndex(AlteredTableInfo *tab, Relation rel,
  */
 static void
 ATExecAddConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
-					Constraint *newConstraint, bool recurse, LOCKMODE lockmode)
+					Constraint *newConstraint, bool recurse, LOCKMODE lockmode, bool enforced)
 {
 	Assert(IsA(newConstraint, Constraint));
 
@@ -4958,7 +4958,7 @@ ATExecAddConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 										 RelationGetNamespace(rel),
 										 NIL);
 
-			ATAddForeignKeyConstraint(tab, rel, newConstraint, lockmode);
+			ATAddForeignKeyConstraint(tab, rel, newConstraint, lockmode, enforced);
 			break;
 
 		default:
@@ -5088,7 +5088,7 @@ ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
  */
 static void
 ATAddForeignKeyConstraint(AlteredTableInfo *tab, Relation rel,
-						  Constraint *fkconstraint, LOCKMODE lockmode)
+						  Constraint *fkconstraint, LOCKMODE lockmode, bool enforced)
 {
 	Relation	pkrel;
 	int16		pkattnum[INDEX_MAX_KEYS];
@@ -5344,9 +5344,10 @@ ATAddForeignKeyConstraint(AlteredTableInfo *tab, Relation rel,
 
 	/*
 	 * Tell Phase 3 to check that the constraint is satisfied by existing rows
-	 * (we can skip this during table creation).
+	 * (we can skip this during table creation). We also skip the check if
+	 * we are adding a foreign key and specifying NOT ENFORCED.
 	 */
-	if (!fkconstraint->skip_validation)
+	if (!fkconstraint->skip_validation && enforced)
 	{
 		NewConstraint *newcon;
 
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 9ec75f7..62222fb 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -1727,11 +1727,12 @@ alter_table_cmd:
 					$$ = (Node *)n;
 				}
 			/* ALTER TABLE <name> ADD CONSTRAINT ... */
-			| ADD_P TableConstraint
+			| ADD_P TableConstraint TableConstraintEnforcement
 				{
 					AlterTableCmd *n = makeNode(AlterTableCmd);
 					n->subtype = AT_AddConstraint;
 					n->def = $2;
+					n->enforced = $3;
 					$$ = (Node *)n;
 				}
 			/* ALTER TABLE <name> DROP CONSTRAINT IF EXISTS <name> [RESTRICT|CASCADE] */
@@ -1942,6 +1943,10 @@ alter_using:
 			| /* EMPTY */				{ $$ = NULL; }
 		;
 
+TableConstraintEnforcement:
+			ENFORCED								{ $$ = TRUE; }
+			| NOT ENFORCED							{ $$ = FALSE; }
+
 reloptions:
 		  	'(' reloption_list ')'					{ $$ = $2; }
 		;
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 8b34b76..b3916b2 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1179,6 +1179,7 @@ typedef struct AlterTableCmd	/* one subcommand of an ALTER TABLE */
 	Node	   *transform;		/* transformation expr for ALTER TYPE */
 	DropBehavior behavior;		/* RESTRICT or CASCADE for DROP cases */
 	bool		missing_ok;		/* skip error if missing? */
+	bool		enforced;		/* Whether or not we perform check */
 } AlterTableCmd;