diff --git a/sync/device.c b/sync/device.c
index 8738835..cf4e4a5 100644
--- a/sync/device.c
+++ b/sync/device.c
@@ -114,6 +114,8 @@ static int get_track_data(const struct sync_device *d, struct sync_track *t)
 
 	fread(&t->num_keys, sizeof(size_t), 1, fp);
 	t->keys = malloc(sizeof(struct track_key) * t->num_keys);
+	if (!t->keys)
+		return 1;
 
 	for (i = 0; i < (int)t->num_keys; ++i) {
 		struct track_key *key = t->keys + i;
@@ -194,8 +196,7 @@ static int handle_set_key_cmd(SOCKET sock, struct sync_data *data)
 	assert(type < KEY_TYPE_COUNT);
 	assert(track < data->num_tracks);
 	key.type = (enum key_type)type;
-	sync_set_key(data->tracks[track], &key);
-	return 1;
+	return !sync_set_key(data->tracks[track], &key);
 }
 
 static int handle_del_key_cmd(SOCKET sock, struct sync_data *data)
@@ -210,8 +211,7 @@ static int handle_del_key_cmd(SOCKET sock, struct sync_data *data)
 	row = ntohl(row);
 
 	assert(track < data->num_tracks);
-	sync_del_key(data->tracks[track], row);
-	return 1;
+	return !sync_del_key(data->tracks[track], row);
 }
 
 static int purge_and_rerequest(struct sync_device *d)
diff --git a/sync/track.c b/sync/track.c
index 6f069ce..8160b46 100644
--- a/sync/track.c
+++ b/sync/track.c
@@ -79,29 +79,39 @@ int sync_find_key(const struct sync_track *t, int row)
 }
 
 #ifndef SYNC_PLAYER
-void sync_set_key(struct sync_track *t, const struct track_key *k)
+int sync_set_key(struct sync_track *t, const struct track_key *k)
 {
 	int idx = sync_find_key(t, k->row);
 	if (idx < 0) {
+		void *tmp;
 		idx = -idx - 1;
+		tmp = realloc(t->keys, sizeof(struct track_key) *
+		    (t->num_keys + 1));
+		if (!tmp)
+			return -1;
 		t->num_keys++;
-		t->keys = realloc(t->keys, sizeof(struct track_key) *
-		    t->num_keys);
-		assert(t->keys);
+		t->keys = tmp;
 		memmove(t->keys + idx + 1, t->keys + idx,
 		    sizeof(struct track_key) * (t->num_keys - idx - 1));
 	}
 	t->keys[idx] = *k;
+	return 0;
 }
 
-void sync_del_key(struct sync_track *t, int pos)
+int sync_del_key(struct sync_track *t, int pos)
 {
+	void *tmp;
 	int idx = sync_find_key(t, pos);
 	assert(idx >= 0);
 	memmove(t->keys + idx, t->keys + idx + 1,
 	    sizeof(struct track_key) * (t->num_keys - idx - 1));
 	assert(t->keys);
+	tmp = realloc(t->keys, sizeof(struct track_key) *
+	    (t->num_keys - 1));
+	if (t->num_keys != 1 && !tmp)
+		return -1;
 	t->num_keys--;
-	t->keys = realloc(t->keys, t->num_keys * sizeof(struct track_key));
+	t->keys = tmp;
+	return 0;
 }
 #endif
diff --git a/sync/track.h b/sync/track.h
index 1946f6d..3611a32 100644
--- a/sync/track.h
+++ b/sync/track.h
@@ -39,8 +39,8 @@ static inline int key_idx_floor(const struct sync_track *t, int row)
 }
 
 #ifndef SYNC_PLAYER
-void sync_set_key(struct sync_track *, const struct track_key *);
-void sync_del_key(struct sync_track *, int);
+int sync_set_key(struct sync_track *, const struct track_key *);
+int sync_del_key(struct sync_track *, int);
 static inline int is_key_frame(const struct sync_track *t, size_t row)
 {
 	return sync_find_key(t, row) >= 0;