diff --git a/idx.h b/idx.h
index a70fd70..6a5c1be 100644
--- a/idx.h
+++ b/idx.h
@@ -49,4 +49,4 @@ typedef struct { uint8_t offseth; uint32_t offsetl; } __attribute__ ((packed)) t
 
 #define TIDMAPSET(__t, __ofs) { (__t)->offseth = (__ofs)>>32; (__t)->offsetl = (__ofs) & 0xffffffff; }
 #define TIDMAPGET(__t) ((__off64_t)(__t)->offseth << 32 | (__t)->offsetl)
-#define TIDMAP(__fdm, __tid) ({ char *_bp = __fdm; tmap_t *_t = (tmap_t *)&_bp[(__tid)*sizeof(tmap_t)]; TIDMAPGET(_t); })
+#define TIDMAP(__fdm, __tid) ({ unsigned char *_bp = __fdm; tmap_t *_t = (tmap_t *)&_bp[(__tid)*sizeof(tmap_t)]; TIDMAPGET(_t); })