diff --git a/include/mruby/irep.h b/include/mruby/irep.h
index d812723ba..e31536e65 100644
--- a/include/mruby/irep.h
+++ b/include/mruby/irep.h
@@ -31,7 +31,7 @@ typedef struct mrb_irep {
 #define MRB_ISEQ_NO_FREE 1
 
 mrb_irep *mrb_add_irep(mrb_state *mrb);
-mrb_value mrb_load_irep(mrb_state*,const unsigned char*);
+mrb_value mrb_load_irep(mrb_state*, const uint8_t*);
 
 #if defined(__cplusplus)
 }  /* extern "C" { */
diff --git a/src/crc.c b/src/crc.c
index 91013c497..70fa60dfb 100644
--- a/src/crc.c
+++ b/src/crc.c
@@ -18,7 +18,7 @@
 #define  CRC_CARRY_BIT      (1 << 24)
 
 uint16_t
-calc_crc_16_ccitt(const unsigned char *src, uint32_t nbytes, uint16_t crc)
+calc_crc_16_ccitt(const uint8_t *src, uint32_t nbytes, uint16_t crc)
 {
   uint32_t ibyte, ibit;
   uint32_t crcwk = crc << 8;