diff --git a/refs/files-backend.c b/refs/files-backend.c
index 9f58ea4858..466cdfe121 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c

@@ -869,8 +869,23 @@ static enum ref_transaction_error lock_raw_ref(struct files_ref_store *refs,
 		 * If the ref did not exist and we are creating it, we have to
 		 * make sure there is no existing packed ref that conflicts
 		 * with refname. This check is deferred so that we can batch it.
+		 *
+		 * For case-insensitive filesystems, we should also check for F/D
+		 * conflicts between 'foo' and 'Foo/bar'. So let's lowercase
+		 * the refname.
 		 */
-		item = string_list_append(refnames_to_check, refname);
+		if (ignore_case) {
+			struct strbuf lower = STRBUF_INIT;
+
+			strbuf_addstr(&lower, refname);
+			strbuf_tolower(&lower);
+
+			item = string_list_append(refnames_to_check, lower.buf);
+			strbuf_release(&lower);

+		} else {
+			item = string_list_append(refnames_to_check, refname);
+		}
+
 		item->util = xmalloc(sizeof(update_idx));
 		memcpy(item->util, &update_idx, sizeof(update_idx));
 	}

diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index 57f60da81b..84dc68e5f3 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh

@@ -53,6 +53,12 @@ test_expect_success "clone and setup child repos" '
 		cd case_sensitive &&
 		git branch branch1 &&
 		git branch bRanch1
+	) &&
+	git clone --ref-format=reftable . case_sensitive_fd &&
+	(
+		cd case_sensitive_fd &&
+		git branch foo/bar &&
+		git branch Foo
 	)
 '
 

@@ -1546,6 +1552,20 @@ test_expect_success CASE_INSENSITIVE_FS,REFFILES 'existing references in a case
 	)
 '
 
+test_expect_success CASE_INSENSITIVE_FS,REFFILES 'F/D conflict on case insensitive filesystem' '
+	test_when_finished rm -rf case_insensitive &&
+	(
+		git init --bare case_insensitive &&
+		cd case_insensitive &&
+		git remote add origin -- ../case_sensitive_fd &&
+		test_must_fail git fetch -f origin "refs/heads/*:refs/heads/*" 2>err &&
+		test_grep "failed: refname conflict" err &&
+		git rev-parse refs/heads/main >expect &&
+		git rev-parse refs/heads/foo/bar >actual &&
+		test_cmp expect actual
+	)
+'