diff --git a/src/index.c b/src/index.c
index 096d122b1..606a431a4 100644
--- a/src/index.c
+++ b/src/index.c
@@ -616,14 +616,14 @@ static int index_entry_reuc_init(git_index_reuc_entry **reuc_out,
 	if (reuc->path == NULL)
 		return -1;
 
-	reuc->mode[0] = ancestor_mode;
-	git_oid_cpy(&reuc->oid[0], ancestor_oid);
+	if ((reuc->mode[0] = ancestor_mode) > 0)
+		git_oid_cpy(&reuc->oid[0], ancestor_oid);
 
-	reuc->mode[1] = our_mode;
-	git_oid_cpy(&reuc->oid[1], our_oid);
+	if ((reuc->mode[1] = our_mode) > 0)
+		git_oid_cpy(&reuc->oid[1], our_oid);
 
-	reuc->mode[2] = their_mode;
-	git_oid_cpy(&reuc->oid[2], their_oid);
+	if ((reuc->mode[2] = their_mode) > 0)
+		git_oid_cpy(&reuc->oid[2], their_oid);
 
 	*reuc_out = reuc;
 	return 0;
diff --git a/tests-clar/index/reuc.c b/tests-clar/index/reuc.c
index 3a139aa5d..2062b51d3 100644
--- a/tests-clar/index/reuc.c
+++ b/tests-clar/index/reuc.c
@@ -31,6 +31,56 @@ void test_index_reuc__cleanup(void)
 	cl_git_sandbox_cleanup();
 }
 
+void test_index_reuc__add(void)
+{
+	git_oid ancestor_oid, our_oid, their_oid;
+	const git_index_reuc_entry *reuc;
+
+	git_oid_fromstr(&ancestor_oid, ONE_ANCESTOR_OID);
+	git_oid_fromstr(&our_oid, ONE_OUR_OID);
+	git_oid_fromstr(&their_oid, ONE_THEIR_OID);
+
+	cl_git_pass(git_index_reuc_add(repo_index, "newfile.txt",
+		0100644, &ancestor_oid,
+		0100644, &our_oid,
+		0100644, &their_oid));
+
+	cl_assert(reuc = git_index_reuc_get_bypath(repo_index, "newfile.txt"));
+
+	cl_assert(strcmp(reuc->path, "newfile.txt") == 0);
+	cl_assert(reuc->mode[0] == 0100644);
+	cl_assert(reuc->mode[1] == 0100644);
+	cl_assert(reuc->mode[2] == 0100644);
+	cl_assert(git_oid_cmp(&reuc->oid[0], &ancestor_oid) == 0);
+	cl_assert(git_oid_cmp(&reuc->oid[1], &our_oid) == 0);
+	cl_assert(git_oid_cmp(&reuc->oid[2], &their_oid) == 0);
+}
+
+void test_index_reuc__add_no_ancestor(void)
+{
+	git_oid ancestor_oid, our_oid, their_oid;
+	const git_index_reuc_entry *reuc;
+
+	memset(&ancestor_oid, 0x0, sizeof(git_oid));
+	git_oid_fromstr(&our_oid, ONE_OUR_OID);
+	git_oid_fromstr(&their_oid, ONE_THEIR_OID);
+
+	cl_git_pass(git_index_reuc_add(repo_index, "newfile.txt",
+		0, NULL,
+		0100644, &our_oid,
+		0100644, &their_oid));
+
+	cl_assert(reuc = git_index_reuc_get_bypath(repo_index, "newfile.txt"));
+
+	cl_assert(strcmp(reuc->path, "newfile.txt") == 0);
+	cl_assert(reuc->mode[0] == 0);
+	cl_assert(reuc->mode[1] == 0100644);
+	cl_assert(reuc->mode[2] == 0100644);
+	cl_assert(git_oid_cmp(&reuc->oid[0], &ancestor_oid) == 0);
+	cl_assert(git_oid_cmp(&reuc->oid[1], &our_oid) == 0);
+	cl_assert(git_oid_cmp(&reuc->oid[2], &their_oid) == 0);
+}
+
 void test_index_reuc__read_bypath(void)
 {
 	const git_index_reuc_entry *reuc;