diff --git a/mrbgems/mruby-io/src/file.c b/mrbgems/mruby-io/src/file.c
index 589f1be14..8f195aa70 100644
--- a/mrbgems/mruby-io/src/file.c
+++ b/mrbgems/mruby-io/src/file.c
@@ -381,7 +381,7 @@ mrb_file__gethome(mrb_state *mrb, mrb_value klass)
   char *pathp = RSTRING_PTR(path);
   const char *const pathend = pathp + RSTRING_LEN(path);
   for (;;) {
-    pathp = memchr((void*)pathp, '\\', (size_t)(pathend - pathp));
+    pathp = (char*)memchr((void*)pathp, '\\', (size_t)(pathend - pathp));
     if (!pathp) break;
     *pathp++ = '/';
   }
diff --git a/mrbgems/mruby-io/test/mruby_io_test.c b/mrbgems/mruby-io/test/mruby_io_test.c
index d47e20cad..f11c960c2 100644
--- a/mrbgems/mruby-io/test/mruby_io_test.c
+++ b/mrbgems/mruby-io/test/mruby_io_test.c
@@ -257,7 +257,7 @@ mrb_mruby_io_gem_test(mrb_state* mrb)
     char *pathp = RSTRING_PTR(path);
     const char *const pathend = pathp + RSTRING_LEN(path);
     for (;;) {
-      pathp = memchr(pathp, '\\', pathend - pathp);
+      pathp = (char*)memchr(pathp, '\\', pathend - pathp);
       if (!pathp) break;
       *pathp++ = '/';
     }