diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 3147dddf28..7808241d3f 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -11271,6 +11271,11 @@ ATExecValidateConstraint(List **wqueue, Relation rel, char *constrName,
  * transformColumnNameList - transform list of column names
  *
  * Lookup each name and return its attnum and, optionally, type OID
+ *
+ * Note: the name of this function suggests that it's general-purpose,
+ * but actually it's only used to look up names appearing in foreign-key
+ * clauses.  The error messages would need work to use it in other cases,
+ * and perhaps the validity checks as well.
  */
 static int
 transformColumnNameList(Oid relId, List *colList,
@@ -11284,6 +11289,7 @@ transformColumnNameList(Oid relId, List *colList,
 	{
 		char	   *attname = strVal(lfirst(l));
 		HeapTuple	atttuple;
+		Form_pg_attribute attform;
 
 		atttuple = SearchSysCacheAttName(relId, attname);
 		if (!HeapTupleIsValid(atttuple))
@@ -11291,14 +11297,19 @@ transformColumnNameList(Oid relId, List *colList,
 					(errcode(ERRCODE_UNDEFINED_COLUMN),
 					 errmsg("column \"%s\" referenced in foreign key constraint does not exist",
 							attname)));
+		attform = (Form_pg_attribute) GETSTRUCT(atttuple);
+		if (attform->attnum < 0)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("system columns cannot be used in foreign keys")));
 		if (attnum >= INDEX_MAX_KEYS)
 			ereport(ERROR,
 					(errcode(ERRCODE_TOO_MANY_COLUMNS),
 					 errmsg("cannot have more than %d keys in a foreign key",
 							INDEX_MAX_KEYS)));
-		attnums[attnum] = ((Form_pg_attribute) GETSTRUCT(atttuple))->attnum;
+		attnums[attnum] = attform->attnum;
 		if (atttypids != NULL)
-			atttypids[attnum] = ((Form_pg_attribute) GETSTRUCT(atttuple))->atttypid;
+			atttypids[attnum] = attform->atttypid;
 		ReleaseSysCache(atttuple);
 		attnum++;
 	}
diff --git a/src/test/regress/expected/foreign_key.out b/src/test/regress/expected/foreign_key.out
index 2f9c083539..55f7158c1a 100644
--- a/src/test/regress/expected/foreign_key.out
+++ b/src/test/regress/expected/foreign_key.out
@@ -795,15 +795,16 @@ SELECT * FROM FKTABLE ORDER BY id;
 
 DROP TABLE FKTABLE;
 DROP TABLE PKTABLE;
-CREATE TABLE PKTABLE (ptest1 int PRIMARY KEY);
+-- Test some invalid FK definitions
+CREATE TABLE PKTABLE (ptest1 int PRIMARY KEY, someoid oid);
 CREATE TABLE FKTABLE_FAIL1 ( ftest1 int, CONSTRAINT fkfail1 FOREIGN KEY (ftest2) REFERENCES PKTABLE);
 ERROR:  column "ftest2" referenced in foreign key constraint does not exist
 CREATE TABLE FKTABLE_FAIL2 ( ftest1 int, CONSTRAINT fkfail1 FOREIGN KEY (ftest1) REFERENCES PKTABLE(ptest2));
 ERROR:  column "ptest2" referenced in foreign key constraint does not exist
-DROP TABLE FKTABLE_FAIL1;
-ERROR:  table "fktable_fail1" does not exist
-DROP TABLE FKTABLE_FAIL2;
-ERROR:  table "fktable_fail2" does not exist
+CREATE TABLE FKTABLE_FAIL3 ( ftest1 int, CONSTRAINT fkfail1 FOREIGN KEY (tableoid) REFERENCES PKTABLE(someoid));
+ERROR:  system columns cannot be used in foreign keys
+CREATE TABLE FKTABLE_FAIL4 ( ftest1 oid, CONSTRAINT fkfail1 FOREIGN KEY (ftest1) REFERENCES PKTABLE(tableoid));
+ERROR:  system columns cannot be used in foreign keys
 DROP TABLE PKTABLE;
 -- Test for referencing column number smaller than referenced constraint
 CREATE TABLE PKTABLE (ptest1 int, ptest2 int, UNIQUE(ptest1, ptest2));
diff --git a/src/test/regress/sql/foreign_key.sql b/src/test/regress/sql/foreign_key.sql
index 90f6db7f21..22e177f89b 100644
--- a/src/test/regress/sql/foreign_key.sql
+++ b/src/test/regress/sql/foreign_key.sql
@@ -490,12 +490,13 @@ SELECT * FROM FKTABLE ORDER BY id;
 DROP TABLE FKTABLE;
 DROP TABLE PKTABLE;
 
-CREATE TABLE PKTABLE (ptest1 int PRIMARY KEY);
+-- Test some invalid FK definitions
+CREATE TABLE PKTABLE (ptest1 int PRIMARY KEY, someoid oid);
 CREATE TABLE FKTABLE_FAIL1 ( ftest1 int, CONSTRAINT fkfail1 FOREIGN KEY (ftest2) REFERENCES PKTABLE);
 CREATE TABLE FKTABLE_FAIL2 ( ftest1 int, CONSTRAINT fkfail1 FOREIGN KEY (ftest1) REFERENCES PKTABLE(ptest2));
+CREATE TABLE FKTABLE_FAIL3 ( ftest1 int, CONSTRAINT fkfail1 FOREIGN KEY (tableoid) REFERENCES PKTABLE(someoid));
+CREATE TABLE FKTABLE_FAIL4 ( ftest1 oid, CONSTRAINT fkfail1 FOREIGN KEY (ftest1) REFERENCES PKTABLE(tableoid));
 
-DROP TABLE FKTABLE_FAIL1;
-DROP TABLE FKTABLE_FAIL2;
 DROP TABLE PKTABLE;
 
 -- Test for referencing column number smaller than referenced constraint