diff --git a/src/backend/utils/adt/ri_triggers.c b/src/backend/utils/adt/ri_triggers.c
index 6958f991604..5d55a2006ee 100644
--- a/src/backend/utils/adt/ri_triggers.c
+++ b/src/backend/utils/adt/ri_triggers.c
@@ -34,6 +34,7 @@
 #include "catalog/pg_am_d.h"
 #include "catalog/pg_collation.h"
 #include "catalog/pg_constraint.h"
+#include "catalog/pg_index.h"
 #include "catalog/pg_namespace.h"
 #include "commands/trigger.h"
 #include "executor/executor.h"
@@ -100,6 +101,14 @@
 
 typedef struct FastPathMeta FastPathMeta;
 
+/* Eligibility checks that require the referenced table and index to be open. */
+typedef enum RI_FastPathState
+{
+	RI_FASTPATH_UNKNOWN,
+	RI_FASTPATH_USABLE,
+	RI_FASTPATH_UNUSABLE
+} RI_FastPathState;
+
 /*
  * RI_ConstraintInfo
  *
@@ -143,7 +152,7 @@ typedef struct RI_ConstraintInfo
 
 	Oid			conindid;
 	bool		pk_is_partitioned;
-	bool		pk_index_is_btree;	/* is conindid a btree index? */
+	RI_FastPathState fastpath_state;	/* populated lazily under lock */
 
 	FastPathMeta *fpmeta;
 } RI_ConstraintInfo;
@@ -281,7 +290,7 @@ static bool ri_PerformCheck(const RI_ConstraintInfo *riinfo,
 							TupleTableSlot *oldslot, TupleTableSlot *newslot,
 							bool is_restrict,
 							bool detectNewRows, int expect_OK);
-static void ri_FastPathCheck(RI_ConstraintInfo *riinfo,
+static bool ri_FastPathCheck(RI_ConstraintInfo *riinfo,
 							 Relation fk_rel, TupleTableSlot *newslot);
 static bool ri_FastPathProbeOne(Relation pk_rel, Relation idx_rel,
 								IndexScanDesc scandesc, TupleTableSlot *slot,
@@ -290,6 +299,8 @@ static bool ri_FastPathProbeOne(Relation pk_rel, Relation idx_rel,
 static bool ri_LockPKTuple(Relation pk_rel, TupleTableSlot *slot, Snapshot snap,
 						   bool *concurrently_updated);
 static bool ri_fastpath_is_applicable(const RI_ConstraintInfo *riinfo);
+static bool ri_check_fastpath_index(RI_ConstraintInfo *riinfo,
+									Relation pk_rel, Relation idx_rel);
 static void ri_CheckPermissions(Relation query_rel);
 static bool recheck_matched_pk_tuple(Relation idxrel, ScanKeyData *skeys,
 									 int nkeys, TupleTableSlot *new_slot);
@@ -416,14 +427,13 @@ RI_FKey_check(TriggerData *trigdata)
 	 * lock.  This is semantically equivalent to the SPI path below but avoids
 	 * the per-row executor overhead.
 	 *
-	 * ri_FastPathCheck() reports the violation itself (via ereport) if no
-	 * matching PK row is found, so it only returns on success.
+	 * ri_FastPathCheck() reports the violation itself if no matching PK row
+	 * is found.  It returns false if the index checks made after opening the
+	 * relations require a SPI fallback.
 	 */
-	if (ri_fastpath_is_applicable(riinfo))
-	{
-		ri_FastPathCheck(riinfo, fk_rel, newslot);
+	if (ri_fastpath_is_applicable(riinfo) &&
+		ri_FastPathCheck(riinfo, fk_rel, newslot))
 		return PointerGetDatum(NULL);
-	}
 
 	SPI_connect();
 
@@ -2429,8 +2439,7 @@ ri_LoadConstraintInfo(Oid constraintOid)
 	riinfo->conindid = conForm->conindid;
 	riinfo->pk_is_partitioned =
 		(get_rel_relkind(riinfo->pk_relid) == RELKIND_PARTITIONED_TABLE);
-	riinfo->pk_index_is_btree =
-		(get_rel_relam(riinfo->conindid) == BTREE_AM_OID);
+	riinfo->fastpath_state = RI_FASTPATH_UNKNOWN;
 
 	ReleaseSysCache(tup);
 
@@ -2739,10 +2748,11 @@ ri_PerformCheck(const RI_ConstraintInfo *riinfo,
  *		Perform per row FK existence check via direct index probe,
  *		bypassing SPI.
  *
- * If no matching PK row exists, report the violation via ri_ReportViolation(),
- * otherwise, the function returns normally.
+ * Return false if the index is unsuitable, so the caller can use SPI.
+ * Otherwise, report any violation via ri_ReportViolation(), or return true
+ * after a successful check.
  */
-static void
+static bool
 ri_FastPathCheck(RI_ConstraintInfo *riinfo,
 				 Relation fk_rel, TupleTableSlot *newslot)
 {
@@ -2776,6 +2786,13 @@ ri_FastPathCheck(RI_ConstraintInfo *riinfo,
 
 	idx_rel = index_open(riinfo->conindid, AccessShareLock);
 
+	if (!ri_check_fastpath_index(riinfo, pk_rel, idx_rel))
+	{
+		index_close(idx_rel, NoLock);
+		table_close(pk_rel, NoLock);
+		return false;
+	}
+
 	/*
 	 * Only now take the snapshot the scan will use.  Acquiring it before
 	 * table_open() would let an unbounded amount of time pass while we wait
@@ -2840,6 +2857,7 @@ ri_FastPathCheck(RI_ConstraintInfo *riinfo,
 
 	index_close(idx_rel, NoLock);
 	table_close(pk_rel, NoLock);
+	return true;
 }
 
 /*
@@ -2954,6 +2972,10 @@ ri_LockPKTuple(Relation pk_rel, TupleTableSlot *slot, Snapshot snap,
 	return false;				/* keep compiler quiet */
 }
 
+/*
+ * Apply the checks that do not require opening the referenced index.  An
+ * unknown state still needs ri_check_fastpath_index() before using it.
+ */
 static bool
 ri_fastpath_is_applicable(const RI_ConstraintInfo *riinfo)
 {
@@ -2973,6 +2995,29 @@ ri_fastpath_is_applicable(const RI_ConstraintInfo *riinfo)
 	if (riinfo->hasperiod)
 		return false;
 
+	return riinfo->fastpath_state != RI_FASTPATH_UNUSABLE;
+}
+
+/*
+ * Check index-dependent eligibility lazily, like fast-path scan metadata.
+ * Cache both success and failure until the constraint information is reloaded.
+ *
+ * The caller has locked the referenced table, reloaded conindid, and opened
+ * the index.  Looking up index properties in ri_LoadConstraintInfo() would
+ * race with REINDEX CONCURRENTLY dropping an index read before that lock.
+ * The index-property checks use the held relation descriptors.
+ */
+static bool
+ri_check_fastpath_index(RI_ConstraintInfo *riinfo,
+						Relation pk_rel, Relation idx_rel)
+{
+	/* Opening the index can have processed further invalidations. */
+	if (!riinfo->valid)
+		riinfo = ri_LoadConstraintInfo(riinfo->constraint_id);
+
+	if (riinfo->fastpath_state != RI_FASTPATH_UNKNOWN)
+		return riinfo->fastpath_state == RI_FASTPATH_USABLE;
+
 	/*
 	 * The fast path probes the referenced index directly.  A foreign key's
 	 * referenced index need not be a primary key; transformFkeyCheckAttrs()
@@ -2980,9 +3025,29 @@ ri_fastpath_is_applicable(const RI_ConstraintInfo *riinfo)
 	 * could reach here.  Restrict the fast path to btree; other access
 	 * methods fall back to SPI.
 	 */
-	if (!riinfo->pk_index_is_btree)
+	if (idx_rel->rd_rel->relam != BTREE_AM_OID)
+	{
+		riinfo->fastpath_state = RI_FASTPATH_UNUSABLE;
 		return false;
+	}
 
+	/*
+	 * Leave comparisons with a different index and referenced-column
+	 * collation to SPI.  Map index keys to table attributes because the FK
+	 * columns need not be listed in index order.  Ignore INCLUDE columns.
+	 */
+	for (int i = 0; i < idx_rel->rd_index->indnkeyatts; i++)
+	{
+		AttrNumber	attnum = idx_rel->rd_index->indkey.values[i];
+
+		if (idx_rel->rd_indcollation[i] != RIAttCollation(pk_rel, attnum))
+		{
+			riinfo->fastpath_state = RI_FASTPATH_UNUSABLE;
+			return false;
+		}
+	}
+
+	riinfo->fastpath_state = RI_FASTPATH_USABLE;
 	return true;
 }
 
diff --git a/src/test/regress/expected/collate.icu.utf8.out b/src/test/regress/expected/collate.icu.utf8.out
index eb483b9015e..ff32cf08864 100644
--- a/src/test/regress/expected/collate.icu.utf8.out
+++ b/src/test/regress/expected/collate.icu.utf8.out
@@ -3111,6 +3111,42 @@ CREATE TABLE test11pk (x text COLLATE case_insensitive PRIMARY KEY);
 CREATE TABLE test11fk (x text COLLATE case_sensitive REFERENCES test11pk (x) ON UPDATE CASCADE ON DELETE CASCADE);  -- error
 ERROR:  foreign key constraint "test11fk_x_fkey" cannot be implemented
 DETAIL:  Key columns "x" of the referencing table and "x" of the referenced table have incompatible collations: "case_sensitive" and "case_insensitive".  If either collation is nondeterministic, then both collations have to be the same.
+-- The referenced index's collation can differ from the column's collation.
+-- Use reversed index columns to exercise the index-to-table column mapping.
+CREATE TABLE fk_collation_pk (id int, x text COLLATE case_insensitive);
+CREATE UNIQUE INDEX fk_collation_idx ON fk_collation_pk (x COLLATE "C", id);
+INSERT INTO fk_collation_pk VALUES (1, 'ABC');
+CREATE TABLE fk_collation_fk (id int, x text COLLATE case_insensitive);
+INSERT INTO fk_collation_fk VALUES (1, 'abc');
+-- Lack of SELECT on the PK table forces per-row validation.
+CREATE ROLE regress_fk_collation;
+GRANT USAGE ON SCHEMA collate_tests TO regress_fk_collation;
+GRANT REFERENCES ON fk_collation_pk TO regress_fk_collation;
+ALTER TABLE fk_collation_fk OWNER TO regress_fk_collation;
+SET ROLE regress_fk_collation;
+ALTER TABLE fk_collation_fk ADD CONSTRAINT fk_collation_fkey
+    FOREIGN KEY (id, x) REFERENCES fk_collation_pk (id, x);
+-- Ordinary DML must also use the column's case-insensitive equality.
+INSERT INTO fk_collation_fk VALUES (1, 'aBc');
+INSERT INTO fk_collation_fk VALUES (2, 'abc'); -- fails
+ERROR:  insert or update on table "fk_collation_fk" violates foreign key constraint "fk_collation_fkey"
+DETAIL:  Key (id, x)=(2, abc) is not present in table "fk_collation_pk".
+RESET ROLE;
+DROP TABLE fk_collation_fk, fk_collation_pk;
+REVOKE USAGE ON SCHEMA collate_tests FROM regress_fk_collation;
+DROP ROLE regress_fk_collation;
+-- Conversely, a case-insensitive index must not make the FK comparison
+-- accept unequal values under the column's deterministic collation.
+CREATE TABLE fk_collation_pk (x text COLLATE "C");
+CREATE UNIQUE INDEX fk_collation_idx ON fk_collation_pk (x COLLATE case_insensitive);
+INSERT INTO fk_collation_pk VALUES ('ABC');
+CREATE TABLE fk_collation_fk (x text COLLATE "C",
+    CONSTRAINT fk_collation_fkey FOREIGN KEY (x) REFERENCES fk_collation_pk (x));
+INSERT INTO fk_collation_fk VALUES ('ABC');
+INSERT INTO fk_collation_fk VALUES ('abc'); -- fails
+ERROR:  insert or update on table "fk_collation_fk" violates foreign key constraint "fk_collation_fkey"
+DETAIL:  Key (x)=(abc) is not present in table "fk_collation_pk".
+DROP TABLE fk_collation_fk, fk_collation_pk;
 -- foreign key actions
 -- Some of the behaviors are most easily visible with a
 -- case-insensitive collation.
diff --git a/src/test/regress/sql/collate.icu.utf8.sql b/src/test/regress/sql/collate.icu.utf8.sql
index df57ebc8bc8..d4915c5b14b 100644
--- a/src/test/regress/sql/collate.icu.utf8.sql
+++ b/src/test/regress/sql/collate.icu.utf8.sql
@@ -1115,6 +1115,40 @@ CREATE TABLE test10fk (x text COLLATE case_insensitive REFERENCES test10pk (x) O
 CREATE TABLE test11pk (x text COLLATE case_insensitive PRIMARY KEY);
 CREATE TABLE test11fk (x text COLLATE case_sensitive REFERENCES test11pk (x) ON UPDATE CASCADE ON DELETE CASCADE);  -- error
 
+-- The referenced index's collation can differ from the column's collation.
+-- Use reversed index columns to exercise the index-to-table column mapping.
+CREATE TABLE fk_collation_pk (id int, x text COLLATE case_insensitive);
+CREATE UNIQUE INDEX fk_collation_idx ON fk_collation_pk (x COLLATE "C", id);
+INSERT INTO fk_collation_pk VALUES (1, 'ABC');
+CREATE TABLE fk_collation_fk (id int, x text COLLATE case_insensitive);
+INSERT INTO fk_collation_fk VALUES (1, 'abc');
+-- Lack of SELECT on the PK table forces per-row validation.
+CREATE ROLE regress_fk_collation;
+GRANT USAGE ON SCHEMA collate_tests TO regress_fk_collation;
+GRANT REFERENCES ON fk_collation_pk TO regress_fk_collation;
+ALTER TABLE fk_collation_fk OWNER TO regress_fk_collation;
+SET ROLE regress_fk_collation;
+ALTER TABLE fk_collation_fk ADD CONSTRAINT fk_collation_fkey
+    FOREIGN KEY (id, x) REFERENCES fk_collation_pk (id, x);
+-- Ordinary DML must also use the column's case-insensitive equality.
+INSERT INTO fk_collation_fk VALUES (1, 'aBc');
+INSERT INTO fk_collation_fk VALUES (2, 'abc'); -- fails
+RESET ROLE;
+DROP TABLE fk_collation_fk, fk_collation_pk;
+REVOKE USAGE ON SCHEMA collate_tests FROM regress_fk_collation;
+DROP ROLE regress_fk_collation;
+
+-- Conversely, a case-insensitive index must not make the FK comparison
+-- accept unequal values under the column's deterministic collation.
+CREATE TABLE fk_collation_pk (x text COLLATE "C");
+CREATE UNIQUE INDEX fk_collation_idx ON fk_collation_pk (x COLLATE case_insensitive);
+INSERT INTO fk_collation_pk VALUES ('ABC');
+CREATE TABLE fk_collation_fk (x text COLLATE "C",
+    CONSTRAINT fk_collation_fkey FOREIGN KEY (x) REFERENCES fk_collation_pk (x));
+INSERT INTO fk_collation_fk VALUES ('ABC');
+INSERT INTO fk_collation_fk VALUES ('abc'); -- fails
+DROP TABLE fk_collation_fk, fk_collation_pk;
+
 -- foreign key actions
 -- Some of the behaviors are most easily visible with a
 -- case-insensitive collation.
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index e11d3ae290b..ad4cc50faa2 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2493,6 +2493,7 @@ RIX
 RI_CompareHashEntry
 RI_CompareKey
 RI_ConstraintInfo
+RI_FastPathState
 RI_QueryHashEntry
 RI_QueryKey
 RTEKind