diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 0c116b3..a488c72 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -3147,9 +3147,6 @@ get_index_column_opclass(Oid index_oid, int attno)
 {
 	HeapTuple	tuple;
 	Form_pg_index rd_index PG_USED_FOR_ASSERTS_ONLY;
-	Datum		datum;
-	bool		isnull;
-	oidvector  *indclass;
 	Oid			opclass;

 	/* First we need to know the column's opclass. */
@@ -3163,12 +3160,22 @@ get_index_column_opclass(Oid index_oid, int attno)
 	/* caller is supposed to guarantee this */
 	Assert(attno > 0 && attno <= rd_index->indnatts);

-	datum = SysCacheGetAttr(INDEXRELID, tuple,
-							Anum_pg_index_indclass, &isnull);
-	Assert(!isnull);
+	if (attno >= 1 && attno <= rd_index->indnkeyatts)
+	{
+		oidvector  *indclass;
+		bool		isnull;
+		Datum		datum = SysCacheGetAttr(INDEXRELID, tuple,
+											Anum_pg_index_indclass,
+											&isnull);
+		Assert(!isnull);

-	indclass = ((oidvector *) DatumGetPointer(datum));
-	opclass = indclass->values[attno - 1];
+		indclass = ((oidvector *) DatumGetPointer(datum));
+		opclass = indclass->values[attno - 1];
+	}
+	else
+	{
+		opclass = InvalidOid;
+	}

 	ReleaseSysCache(tuple);