diff --git a/src/backend/utils/adt/ri_triggers.c b/src/backend/utils/adt/ri_triggers.c
index 521ec04f6b8..35067822082 100644
--- a/src/backend/utils/adt/ri_triggers.c
+++ b/src/backend/utils/adt/ri_triggers.c
@@ -31,6 +31,7 @@
 #include "access/tableam.h"
 #include "access/xact.h"
 #include "catalog/index.h"
+#include "catalog/namespace.h"
 #include "catalog/objectaccess.h"
 #include "catalog/pg_am_d.h"
 #include "catalog/pg_collation.h"
@@ -45,6 +46,7 @@
 #include "miscadmin.h"
 #include "parser/parse_coerce.h"
 #include "parser/parse_relation.h"
+#include "tcop/utility.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
 #include "utils/datum.h"
@@ -2789,6 +2791,14 @@ ri_FastPathCheck(RI_ConstraintInfo *riinfo,
 
 	pk_rel = table_open(riinfo->pk_relid, RowShareLock);
 
+	/*
+	 * The row lock taken below is refused in a read-only transaction unless
+	 * the referenced table is temporary, as ExecCheckXactReadOnly() refuses
+	 * the SPI path's SELECT ... FOR KEY SHARE.
+	 */
+	if (XactReadOnly && !isTempNamespace(RelationGetNamespace(pk_rel)))
+		PreventCommandIfReadOnly("SELECT FOR KEY SHARE");
+
 	/*
 	 * Advance the command counter so the check sees the effects of prior
 	 * triggers in this statement, as SPI does when executing the query issued
diff --git a/src/test/regress/expected/foreign_key.out b/src/test/regress/expected/foreign_key.out
index abafaff785a..e2709279eae 100644
--- a/src/test/regress/expected/foreign_key.out
+++ b/src/test/regress/expected/foreign_key.out
@@ -4119,3 +4119,34 @@ DROP TYPE fkint CASCADE;
 NOTICE:  drop cascades to 2 other objects
 DETAIL:  drop cascades to function fkint_in(cstring)
 drop cascades to function fkint_out(fkint)
+-- An FK check locks the referenced row, which a read-only transaction does
+-- not allow unless the referenced table is temporary.
+CREATE TABLE fp_pk_ro (a int PRIMARY KEY);
+INSERT INTO fp_pk_ro VALUES (1);
+CREATE TABLE fp_fk_ro (a int REFERENCES fp_pk_ro DEFERRABLE INITIALLY DEFERRED);
+BEGIN;
+INSERT INTO fp_fk_ro VALUES (1);
+SET TRANSACTION READ ONLY;
+COMMIT;	-- fails
+ERROR:  cannot execute SELECT FOR KEY SHARE in a read-only transaction
+CREATE TEMP TABLE fp_pk_ro_tmp (a int PRIMARY KEY);
+INSERT INTO fp_pk_ro_tmp VALUES (1);
+CREATE TEMP TABLE fp_fk_ro_tmp (a int REFERENCES fp_pk_ro_tmp
+    DEFERRABLE INITIALLY DEFERRED);
+BEGIN;
+INSERT INTO fp_fk_ro_tmp VALUES (1);
+SET TRANSACTION READ ONLY;
+COMMIT;	-- succeeds
+SELECT count(*) FROM fp_fk_ro;
+ count 
+-------
+     0
+(1 row)
+
+SELECT count(*) FROM fp_fk_ro_tmp;
+ count 
+-------
+     1
+(1 row)
+
+DROP TABLE fp_fk_ro, fp_pk_ro, fp_fk_ro_tmp, fp_pk_ro_tmp;
diff --git a/src/test/regress/sql/foreign_key.sql b/src/test/regress/sql/foreign_key.sql
index da62f601b46..a706083948d 100644
--- a/src/test/regress/sql/foreign_key.sql
+++ b/src/test/regress/sql/foreign_key.sql
@@ -3065,3 +3065,24 @@ DROP TABLE pktable_inval;
 DROP CAST (fkint AS int4);
 DROP FUNCTION fkint_to_int4(fkint);
 DROP TYPE fkint CASCADE;
+
+-- An FK check locks the referenced row, which a read-only transaction does
+-- not allow unless the referenced table is temporary.
+CREATE TABLE fp_pk_ro (a int PRIMARY KEY);
+INSERT INTO fp_pk_ro VALUES (1);
+CREATE TABLE fp_fk_ro (a int REFERENCES fp_pk_ro DEFERRABLE INITIALLY DEFERRED);
+BEGIN;
+INSERT INTO fp_fk_ro VALUES (1);
+SET TRANSACTION READ ONLY;
+COMMIT;	-- fails
+CREATE TEMP TABLE fp_pk_ro_tmp (a int PRIMARY KEY);
+INSERT INTO fp_pk_ro_tmp VALUES (1);
+CREATE TEMP TABLE fp_fk_ro_tmp (a int REFERENCES fp_pk_ro_tmp
+    DEFERRABLE INITIALLY DEFERRED);
+BEGIN;
+INSERT INTO fp_fk_ro_tmp VALUES (1);
+SET TRANSACTION READ ONLY;
+COMMIT;	-- succeeds
+SELECT count(*) FROM fp_fk_ro;
+SELECT count(*) FROM fp_fk_ro_tmp;
+DROP TABLE fp_fk_ro, fp_pk_ro, fp_fk_ro_tmp, fp_pk_ro_tmp;