diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 158c594..8a73860 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -6738,6 +6738,23 @@ transformFkeyCheckAttrs(Relation pkrel,
 	bool		found_deferrable = false;
 	List	   *indexoidlist;
 	ListCell   *indexoidscan;
+	int			i,
+				j;
+
+	/*
+	 * We'll disallow foreign keys from being defined which reference indexes
+	 * that have duplicated columns.
+	 */
+	for (i = 0; i < numattrs; i++)
+	{
+		for (j = i + 1; j < numattrs; j++)
+		{
+			if (attnums[i] == attnums[j])
+				ereport(ERROR,
+					(errcode(ERRCODE_INVALID_FOREIGN_KEY),
+					errmsg("a foreign key cannot contain duplicate column references")));
+		}
+	}
 
 	/*
 	 * Get the list of index OIDs for the table from the relcache, and look up
@@ -6750,8 +6767,6 @@ transformFkeyCheckAttrs(Relation pkrel,
 	{
 		HeapTuple	indexTuple;
 		Form_pg_index indexStruct;
-		int			i,
-					j;
 
 		indexoid = lfirst_oid(indexoidscan);
 		indexTuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(indexoid));
@@ -6782,7 +6797,10 @@ transformFkeyCheckAttrs(Relation pkrel,
 
 			/*
 			 * The given attnum list may match the index columns in any order.
-			 * Check that each list is a subset of the other.
+			 *
+			 * We already know that attnums is free of duplicate values per the
+			 * test at the start of this function, so we can skip on testing if
+			 * the attnums is a subset of the index key values.
 			 */
 			for (i = 0; i < numattrs; i++)
 			{
@@ -6791,6 +6809,7 @@ transformFkeyCheckAttrs(Relation pkrel,
 				{
 					if (attnums[i] == indexStruct->indkey.values[j])
 					{
+						opclasses[i] = indclass->values[j];
 						found = true;
 						break;
 					}
@@ -6798,24 +6817,6 @@ transformFkeyCheckAttrs(Relation pkrel,
 				if (!found)
 					break;
 			}
-			if (found)
-			{
-				for (i = 0; i < numattrs; i++)
-				{
-					found = false;
-					for (j = 0; j < numattrs; j++)
-					{
-						if (attnums[j] == indexStruct->indkey.values[i])
-						{
-							opclasses[j] = indclass->values[i];
-							found = true;
-							break;
-						}
-					}
-					if (!found)
-						break;
-				}
-			}
 
 			/*
 			 * Refuse to use a deferrable unique/primary key.  This is per SQL
diff --git a/src/test/regress/expected/foreign_key.out b/src/test/regress/expected/foreign_key.out
index 0299bfe..d23e49b 100644
--- a/src/test/regress/expected/foreign_key.out
+++ b/src/test/regress/expected/foreign_key.out
@@ -732,6 +732,15 @@ ERROR:  there is no unique constraint matching given keys for referenced table "
 DROP TABLE FKTABLE_FAIL1;
 ERROR:  table "fktable_fail1" does not exist
 DROP TABLE PKTABLE;
+-- Test to ensure foreign keys that reference unique constraints with duplicate
+-- column references are disallowed.
+CREATE TABLE PKTABLE (ptest1 int);
+CREATE UNIQUE INDEX ON PKTABLE (ptest1, ptest1);
+CREATE TABLE FKTABLE_FAIL1 (ftest1 int, ftest2 int);
+ALTER TABLE FKTABLE_FAIL1 ADD CONSTRAINT fk FOREIGN KEY (ftest1, ftest2) REFERENCES PKTABLE(ptest1,ptest1);
+ERROR:  a foreign key cannot contain duplicate column references
+DROP TABLE FKTABLE_FAIL1;
+DROP TABLE PKTABLE;
 --
 -- Tests for mismatched types
 --
diff --git a/src/test/regress/sql/foreign_key.sql b/src/test/regress/sql/foreign_key.sql
index 531c881..976f402 100644
--- a/src/test/regress/sql/foreign_key.sql
+++ b/src/test/regress/sql/foreign_key.sql
@@ -439,6 +439,16 @@ CREATE TABLE FKTABLE_FAIL1 (ftest1 int REFERENCES pktable(ptest1));
 DROP TABLE FKTABLE_FAIL1;
 DROP TABLE PKTABLE;
 
+-- Test to ensure foreign keys that reference unique constraints with duplicate
+-- column references are disallowed.
+CREATE TABLE PKTABLE (ptest1 int);
+CREATE UNIQUE INDEX ON PKTABLE (ptest1, ptest1);
+CREATE TABLE FKTABLE_FAIL1 (ftest1 int, ftest2 int);
+ALTER TABLE FKTABLE_FAIL1 ADD CONSTRAINT fk FOREIGN KEY (ftest1, ftest2) REFERENCES PKTABLE(ptest1,ptest1);
+
+DROP TABLE FKTABLE_FAIL1;
+DROP TABLE PKTABLE;
+
 --
 -- Tests for mismatched types
 --