diff --git a/src/backend/libpq/be-fsstubs.c b/src/backend/libpq/be-fsstubs.c
index 5804532881..2ffdba53d6 100644
--- a/src/backend/libpq/be-fsstubs.c
+++ b/src/backend/libpq/be-fsstubs.c
@@ -245,6 +245,8 @@ be_lo_creat(PG_FUNCTION_ARGS)
 {
 	Oid			lobjId;
 
+	PreventCommandIfReadOnly("lo_creat");
+
 	lo_cleanup_needed = true;
 	lobjId = inv_create(InvalidOid);
 
@@ -256,6 +258,8 @@ be_lo_create(PG_FUNCTION_ARGS)
 {
 	Oid			lobjId = PG_GETARG_OID(0);
 
+	PreventCommandIfReadOnly("lo_create");
+
 	lo_cleanup_needed = true;
 	lobjId = inv_create(lobjId);
 
@@ -306,6 +310,8 @@ be_lo_unlink(PG_FUNCTION_ARGS)
 {
 	Oid			lobjId = PG_GETARG_OID(0);
 
+	PreventCommandIfReadOnly("lo_unlink");
+
 	/*
 	 * Must be owner of the large object.  It would be cleaner to check this
 	 * in inv_drop(), but we want to throw the error before not after closing
@@ -368,6 +374,8 @@ be_lowrite(PG_FUNCTION_ARGS)
 	int			bytestowrite;
 	int			totalwritten;
 
+	PreventCommandIfReadOnly("lowrite");
+
 	bytestowrite = VARSIZE_ANY_EXHDR(wbuf);
 	totalwritten = lo_write(fd, VARDATA_ANY(wbuf), bytestowrite);
 	PG_RETURN_INT32(totalwritten);
@@ -413,6 +421,8 @@ lo_import_internal(text *filename, Oid lobjOid)
 	LargeObjectDesc *lobj;
 	Oid			oid;
 
+	PreventCommandIfReadOnly("lo_import");
+
 	/*
 	 * open the file to be read in
 	 */
@@ -539,6 +549,8 @@ lo_truncate_internal(int32 fd, int64 len)
 {
 	LargeObjectDesc *lobj;
 
+	PreventCommandIfReadOnly("lo_truncate");
+
 	if (fd < 0 || fd >= cookies_size || cookies[fd] == NULL)
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_OBJECT),
@@ -815,6 +827,8 @@ be_lo_from_bytea(PG_FUNCTION_ARGS)
 	LargeObjectDesc *loDesc;
 	int			written PG_USED_FOR_ASSERTS_ONLY;
 
+	PreventCommandIfReadOnly("lo_from_bytea");
+
 	lo_cleanup_needed = true;
 	loOid = inv_create(loOid);
 	loDesc = inv_open(loOid, INV_WRITE, CurrentMemoryContext);
@@ -837,6 +851,8 @@ be_lo_put(PG_FUNCTION_ARGS)
 	LargeObjectDesc *loDesc;
 	int			written PG_USED_FOR_ASSERTS_ONLY;
 
+	PreventCommandIfReadOnly("lo_put");
+
 	lo_cleanup_needed = true;
 	loDesc = inv_open(loOid, INV_WRITE, CurrentMemoryContext);
 
diff --git a/src/test/regress/expected/largeobject.out b/src/test/regress/expected/largeobject.out
index 8e32de04e6..14344edfba 100644
--- a/src/test/regress/expected/largeobject.out
+++ b/src/test/regress/expected/largeobject.out
@@ -506,6 +506,39 @@ SELECT lo_create(2121);
 (1 row)
 
 COMMENT ON LARGE OBJECT 2121 IS 'testing comments';
+-- Test writes on large objects in read-only transactions
+START TRANSACTION READ ONLY;
+SELECT lo_create(42);
+ERROR:  cannot execute lo_create in a read-only transaction
+ROLLBACK;
+START TRANSACTION READ ONLY;
+SELECT lo_creat(42);
+ERROR:  cannot execute lo_creat in a read-only transaction
+ROLLBACK;
+START TRANSACTION READ ONLY;
+SELECT lo_unlink(42);
+ERROR:  cannot execute lo_unlink in a read-only transaction
+ROLLBACK;
+START TRANSACTION READ ONLY;
+SELECT lowrite(42, 'x');
+ERROR:  cannot execute lowrite in a read-only transaction
+ROLLBACK;
+START TRANSACTION READ ONLY;
+SELECT lo_import(:'filename');
+ERROR:  cannot execute lo_import in a read-only transaction
+ROLLBACK;
+START TRANSACTION READ ONLY;
+SELECT lo_truncate(42, 0);
+ERROR:  cannot execute lo_truncate in a read-only transaction
+ROLLBACK;
+START TRANSACTION READ ONLY;
+SELECT lo_from_bytea(0, 'x');
+ERROR:  cannot execute lo_from_bytea in a read-only transaction
+ROLLBACK;
+START TRANSACTION READ ONLY;
+SELECT lo_put(42, 0, 'x');
+ERROR:  cannot execute lo_put in a read-only transaction
+ROLLBACK;
 -- Clean up
 DROP TABLE lotest_stash_values;
 DROP ROLE regress_lo_user;
diff --git a/src/test/regress/sql/largeobject.sql b/src/test/regress/sql/largeobject.sql
index fd3518889e..8b1a2b70c5 100644
--- a/src/test/regress/sql/largeobject.sql
+++ b/src/test/regress/sql/largeobject.sql
@@ -271,6 +271,39 @@ SELECT lo_create(2121);
 
 COMMENT ON LARGE OBJECT 2121 IS 'testing comments';
 
+-- Test writes on large objects in read-only transactions
+START TRANSACTION READ ONLY;
+SELECT lo_create(42);
+ROLLBACK;
+
+START TRANSACTION READ ONLY;
+SELECT lo_creat(42);
+ROLLBACK;
+
+START TRANSACTION READ ONLY;
+SELECT lo_unlink(42);
+ROLLBACK;
+
+START TRANSACTION READ ONLY;
+SELECT lowrite(42, 'x');
+ROLLBACK;
+
+START TRANSACTION READ ONLY;
+SELECT lo_import(:'filename');
+ROLLBACK;
+
+START TRANSACTION READ ONLY;
+SELECT lo_truncate(42, 0);
+ROLLBACK;
+
+START TRANSACTION READ ONLY;
+SELECT lo_from_bytea(0, 'x');
+ROLLBACK;
+
+START TRANSACTION READ ONLY;
+SELECT lo_put(42, 0, 'x');
+ROLLBACK;
+
 -- Clean up
 DROP TABLE lotest_stash_values;