diff --git a/include/mruby/string.h b/include/mruby/string.h
index df6fb25c34..4c25b93467 100644
--- a/include/mruby/string.h
+++ b/include/mruby/string.h
@@ -409,7 +409,7 @@ MRB_API int mrb_str_cmp(mrb_state *mrb, mrb_value str1, mrb_value str2);
 MRB_API char *mrb_str_to_cstr(mrb_state *mrb, mrb_value str);
 
 mrb_value mrb_str_pool(mrb_state *mrb, mrb_value str);
-mrb_int mrb_str_hash(mrb_state *mrb, mrb_value str);
+uint32_t mrb_str_hash(mrb_state *mrb, mrb_value str);
 mrb_value mrb_str_dump(mrb_state *mrb, mrb_value str);
 
 /*
diff --git a/src/string.c b/src/string.c
index 01d706fa38..f50468ccaa 100644
--- a/src/string.c
+++ b/src/string.c
@@ -1467,7 +1467,7 @@ mrb_str_substr(mrb_state *mrb, mrb_value str, mrb_int beg, mrb_int len)
   return str_substr(mrb, str, beg, len);
 }
 
-mrb_int
+uint32_t
 mrb_str_hash(mrb_state *mrb, mrb_value str)
 {
   /* 1-8-7 */
@@ -1480,7 +1480,7 @@ mrb_str_hash(mrb_state *mrb, mrb_value str)
     key = key*65599 + *p;
     p++;
   }
-  return (mrb_int)(key + (key>>5));
+  return (uint32_t)(key + (key>>5));
 }
 
 /* 15.2.10.5.20 */