diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index d263903622..c8c64d9a42 100644
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -721,7 +721,7 @@ DefineIndex(Oid relationId,
 						 errdetail("%s constraints cannot be used when partition keys include expressions.",
 								   constraint_type)));
 
-			for (j = 0; j < indexInfo->ii_NumIndexAttrs; j++)
+			for (j = 0; j < indexInfo->ii_NumIndexKeyAttrs; j++)
 			{
 				if (key->partattrs[i] == indexInfo->ii_IndexAttrNumbers[j])
 				{
diff --git a/src/test/regress/expected/indexing.out b/src/test/regress/expected/indexing.out
index caacf3f799..118f2c78df 100644
--- a/src/test/regress/expected/indexing.out
+++ b/src/test/regress/expected/indexing.out
@@ -1411,3 +1411,6 @@ insert into covidxpart values (4, 1);
 insert into covidxpart values (4, 1);
 ERROR:  duplicate key value violates unique constraint "covidxpart4_a_b_idx"
 DETAIL:  Key (a)=(4) already exists.
+create unique index on covidxpart (b) include (a); -- should fail
+ERROR:  insufficient columns in UNIQUE constraint definition
+DETAIL:  UNIQUE constraint on table "covidxpart" lacks column "a" which is part of the partition key.
diff --git a/src/test/regress/sql/indexing.sql b/src/test/regress/sql/indexing.sql
index 6878cde509..d4a64c18c7 100644
--- a/src/test/regress/sql/indexing.sql
+++ b/src/test/regress/sql/indexing.sql
@@ -756,3 +756,4 @@ create unique index on covidxpart4 (a);
 alter table covidxpart attach partition covidxpart4 for values in (4);
 insert into covidxpart values (4, 1);
 insert into covidxpart values (4, 1);
+create unique index on covidxpart (b) include (a); -- should fail