diff --git src/bin/psql/tab-complete.c src/bin/psql/tab-complete.c
index 7c4933333b..b2b8431bc2 100644
--- src/bin/psql/tab-complete.c
+++ src/bin/psql/tab-complete.c
@@ -785,6 +785,15 @@ static const SchemaQuery Query_for_list_of_collations = {
 "       and pg_catalog.quote_ident(c1.relname)='%s'"\
 "       and pg_catalog.pg_table_is_visible(c1.oid)"
 
+/* the silly-looking length condition is just to eat up the current word */
+#define Query_for_nonvalid_constraint_of_table \
+"SELECT pg_catalog.quote_ident(conname) "\
+"  FROM pg_catalog.pg_class c1, pg_catalog.pg_constraint con "\
+" WHERE c1.oid=conrelid and not convalidated"\
+"       and (%d = pg_catalog.length('%s'))"\
+"       and pg_catalog.quote_ident(c1.relname)='%s'"\
+"       and pg_catalog.pg_table_is_visible(c1.oid)"
+
 #define Query_for_all_table_constraints \
 "SELECT pg_catalog.quote_ident(conname) "\
 "  FROM pg_catalog.pg_constraint c "\
@@ -2107,8 +2116,8 @@ psql_completion(const char *text, int start, int end)
 	else if (Matches("ALTER", "TABLE", MatchAny, "RENAME", "COLUMN|CONSTRAINT", MatchAnyExcept("TO")))
 		COMPLETE_WITH("TO");
 
-	/* If we have ALTER TABLE <sth> DROP, provide COLUMN or CONSTRAINT */
-	else if (Matches("ALTER", "TABLE", MatchAny, "DROP"))
+	/* If we have ALTER TABLE <sth> ADD|DROP, provide COLUMN or CONSTRAINT */
+	else if (Matches("ALTER", "TABLE", MatchAny, "ADD|DROP"))
 		COMPLETE_WITH("COLUMN", "CONSTRAINT");
 	/* If we have ALTER TABLE <sth> DROP COLUMN, provide list of columns */
 	else if (Matches("ALTER", "TABLE", MatchAny, "DROP", "COLUMN"))
@@ -2118,11 +2127,16 @@ psql_completion(const char *text, int start, int end)
 	 * If we have ALTER TABLE <sth> ALTER|DROP|RENAME|VALIDATE CONSTRAINT,
 	 * provide list of constraints
 	 */
-	else if (Matches("ALTER", "TABLE", MatchAny, "ALTER|DROP|RENAME|VALIDATE", "CONSTRAINT"))
+	else if (Matches("ALTER", "TABLE", MatchAny, "ALTER|DROP|RENAME", "CONSTRAINT"))
 	{
 		completion_info_charp = prev3_wd;
 		COMPLETE_WITH_QUERY(Query_for_constraint_of_table);
 	}
+	else if (Matches("ALTER", "TABLE", MatchAny, "VALIDATE", "CONSTRAINT"))
+	{
+		completion_info_charp = prev3_wd;
+		COMPLETE_WITH_QUERY(Query_for_nonvalid_constraint_of_table);
+	}
 	/* ALTER TABLE ALTER [COLUMN] <foo> */
 	else if (Matches("ALTER", "TABLE", MatchAny, "ALTER", "COLUMN", MatchAny) ||
 			 Matches("ALTER", "TABLE", MatchAny, "ALTER", MatchAny))