diff --git a/src/trie.c b/src/trie.c
index 31157789..cae61640 100644
--- a/src/trie.c
+++ b/src/trie.c
@@ -454,10 +454,10 @@ void trie_add_tail(trie_t *self, unsigned char *tail) {
     uchar_array_push(self->tail, '\0');
 }
 
-void trie_set_tail(trie_t *self, unsigned char *tail, int32_t tail_pos) {
+void trie_set_tail(trie_t *self, unsigned char *tail, uint32_t tail_pos) {
     log_debug("Setting tail: %s at pos %d\n", tail, tail_pos);
     size_t tail_len = strlen((char *)tail);
-    size_t num_appends = ((size_t)tail_pos + tail_len) - self->tail->n;
+    ssize_t num_appends = (ssize_t)(tail_pos + tail_len) - self->tail->n;
     int i = 0;
 
     // Pad with 0s if we're short
diff --git a/src/trie.h b/src/trie.h
index ba6a8970..88864f3e 100644
--- a/src/trie.h
+++ b/src/trie.h
@@ -109,7 +109,7 @@ uint32_t trie_add_transition(trie_t *self, uint32_t node_id, unsigned char c);
 void trie_make_room_for(trie_t *self, uint32_t next_id);
 
 void trie_add_tail(trie_t *self, unsigned char *tail);
-void trie_set_tail(trie_t *self, unsigned char *tail, int32_t tail_pos);
+void trie_set_tail(trie_t *self, unsigned char *tail, uint32_t tail_pos);
 int32_t trie_separate_tail(trie_t *self, uint32_t from_index, unsigned char *tail, uint32_t data);
 void trie_tail_merge(trie_t *self, uint32_t old_node_id, unsigned char *suffix, uint32_t data);