diff --git a/core/src-c/runes.c b/core/src-c/runes.c
index b545c59..17d2da3 100644
--- a/core/src-c/runes.c
+++ b/core/src-c/runes.c
@@ -1,9 +1,9 @@
 #include <librr/runes.h>
 
-isz_t rr_distance_to_last_utf8_rune_start(const char *string, usz_t offset)
+isz_t rr_distance_to_last_utf8_rune_start(const char *string, isz_t offset)
 {
     usz_t                       bytes_walked                    = 0;
-    while(bytes_walked < offset)
+    while((offset - bytes_walked) >= 0)
     {
         if(bytes_walked > 4)
             return -1;