diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index ccf4eb7e9b3361ee7eb209180d98ce8df757d92d..0d55f73b0b443b60dccc31096675d40691b3eb56 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -14,6 +14,7 @@
 #include "thread-utils.h"
 #include "packfile.h"
 #include "object-store.h"
+#include "fetch-object.h"
 
 static const char index_pack_usage[] =
 "git index-pack [-v] [-o <index-file>] [--keep | --keep=<msg>] [--verify] [--strict] (<pack-file> | --stdin [--fix-thin] [<pack-file>])";
@@ -1351,6 +1352,25 @@ static void fix_unresolved_deltas(struct hashfile *f)
 		sorted_by_pos[i] = &ref_deltas[i];
 	QSORT(sorted_by_pos, nr_ref_deltas, delta_pos_compare);
 
+	if (repository_format_partial_clone) {
+		/*
+		 * Prefetch the delta bases.
+		 */
+		struct oid_array to_fetch = OID_ARRAY_INIT;
+		for (i = 0; i < nr_ref_deltas; i++) {
+			struct ref_delta_entry *d = sorted_by_pos[i];
+			if (!oid_object_info_extended(the_repository, &d->oid,
+						      NULL,
+						      OBJECT_INFO_FOR_PREFETCH))
+				continue;
+			oid_array_append(&to_fetch, &d->oid);
+		}
+		if (to_fetch.nr)
+			fetch_objects(repository_format_partial_clone,
+				      to_fetch.oid, to_fetch.nr);
+		oid_array_clear(&to_fetch);
+	}
+
 	for (i = 0; i < nr_ref_deltas; i++) {
 		struct ref_delta_entry *d = sorted_by_pos[i];
 		enum object_type type;
@@ -1650,8 +1670,10 @@ int cmd_index_pack(int argc, const char **argv, const char *prefix)
 	int report_end_of_input = 0;
 
 	/*
-	 * index-pack never needs to fetch missing objects, since it only
-	 * accesses the repo to do hash collision checks
+	 * index-pack never needs to fetch missing objects except when
+	 * REF_DELTA bases are missing (which are explicitly handled). It only
+	 * accesses the repo to do hash collision checks and to check which
+	 * REF_DELTA bases need to be fetched.
 	 */
 	fetch_if_missing = 0;
 
diff --git a/t/t5616-partial-clone.sh b/t/t5616-partial-clone.sh
index 7cc0c71556171c807ca53045bcc85bebace3b3b6..f1baf83502093c338c7fe9bec97e69ff25f373ed 100755
--- a/t/t5616-partial-clone.sh
+++ b/t/t5616-partial-clone.sh
@@ -339,4 +339,65 @@ test_expect_success 'when partial cloning, tolerate server not sending target of
 	! test -e "$HTTPD_ROOT_PATH/one-time-sed"
 '
 
+test_expect_success 'tolerate server sending REF_DELTA against missing promisor objects' '
+	SERVER="$HTTPD_DOCUMENT_ROOT_PATH/server" &&
+	rm -rf "$SERVER" repo &&
+	test_create_repo "$SERVER" &&
+	test_config -C "$SERVER" uploadpack.allowfilter 1 &&
+	test_config -C "$SERVER" uploadpack.allowanysha1inwant 1 &&
+
+	# Create a commit with a blob to be used as a delta base.
+	for i in $(test_seq 10)
+	do
+		echo "this is a line" >>"$SERVER/foo.txt"
+	done &&
+	git -C "$SERVER" add foo.txt &&
+	git -C "$SERVER" commit -m bar &&
+	git -C "$SERVER" rev-parse HEAD:foo.txt >deltabase &&
+
+	git -c protocol.version=2 clone --no-checkout \
+		--filter=blob:none $HTTPD_URL/one_time_sed/server repo &&
+
+	# Sanity check to ensure that the client does not have that blob.
+	git -C repo rev-list --objects --exclude-promisor-objects \
+		-- $(cat deltabase) >objlist &&
+	test_line_count = 0 objlist &&
+
+	# Another commit. This commit will be fetched by the client.
+	echo "abcdefghijklmnopqrstuvwxyz" >>"$SERVER/foo.txt" &&
+	git -C "$SERVER" add foo.txt &&
+	git -C "$SERVER" commit -m baz &&
+
+	# Pack a thin pack containing, among other things, HEAD:foo.txt
+	# delta-ed against HEAD^:foo.txt.
+	printf "%s\n--not\n%s\n" \
+		$(git -C "$SERVER" rev-parse HEAD) \
+		$(git -C "$SERVER" rev-parse HEAD^) |
+		git -C "$SERVER" pack-objects --thin --stdout >thin.pack &&
+
+	# Ensure that the pack contains one delta against HEAD^:foo.txt. Since
+	# the delta contains at least 26 novel characters, the size cannot be
+	# contained in 4 bits, so the object header will take up 2 bytes. The
+	# most significant nybble of the first byte is 0b1111 (0b1 to indicate
+	# that the header continues, and 0b111 to indicate REF_DELTA), followed
+	# by any 3 nybbles, then the OID of the delta base.
+	git -C "$SERVER" rev-parse HEAD^:foo.txt >deltabase &&
+	printf "f.,..%s" $(intersperse "," <deltabase) >want &&
+	hex_unpack <thin.pack | intersperse "," >have &&
+	grep $(cat want) have &&
+
+	replace_packfile thin.pack &&
+
+	# Use protocol v2 because the sed command looks for the "packfile"
+	# section header.
+	test_config -C "$SERVER" protocol.version 2 &&
+
+	# Fetch the thin pack and ensure that index-pack is able to handle the
+	# REF_DELTA object with a missing promisor delta base.
+	git -C repo -c protocol.version=2 fetch &&
+
+	# Ensure that the one-time-sed script was used.
+	! test -e "$HTTPD_ROOT_PATH/one-time-sed"
+'
+
 test_done