diff --git a/mrbgems/mruby-dir/src/dir.c b/mrbgems/mruby-dir/src/dir.c
index 174bdcf7a..41efc7097 100644
--- a/mrbgems/mruby-dir/src/dir.c
+++ b/mrbgems/mruby-dir/src/dir.c
@@ -41,7 +41,7 @@ struct mrb_dir {
   DIR *dir;
 };
 
-void
+static void
 mrb_dir_free(mrb_state *mrb, void *ptr)
 {
   struct mrb_dir *mdir = (struct mrb_dir*)ptr;
@@ -55,7 +55,7 @@ mrb_dir_free(mrb_state *mrb, void *ptr)
 
 static struct mrb_data_type mrb_dir_type = { "DIR", mrb_dir_free };
 
-mrb_value
+static mrb_value
 mrb_dir_close(mrb_state *mrb, mrb_value self)
 {
   struct mrb_dir *mdir;
@@ -71,7 +71,7 @@ mrb_dir_close(mrb_state *mrb, mrb_value self)
   return mrb_nil_value();
 }
 
-mrb_value
+static mrb_value
 mrb_dir_init(mrb_state *mrb, mrb_value self)
 {
   DIR *dir;
@@ -99,7 +99,7 @@ mrb_dir_init(mrb_state *mrb, mrb_value self)
   return self;
 }
 
-mrb_value
+static mrb_value
 mrb_dir_delete(mrb_state *mrb, mrb_value klass)
 {
   mrb_value path;
@@ -113,7 +113,7 @@ mrb_dir_delete(mrb_state *mrb, mrb_value klass)
   return mrb_fixnum_value(0);
 }
 
-mrb_value
+static mrb_value
 mrb_dir_existp(mrb_state *mrb, mrb_value klass)
 {
   mrb_value path;
@@ -130,7 +130,7 @@ mrb_dir_existp(mrb_state *mrb, mrb_value klass)
   }
 }
 
-mrb_value
+static mrb_value
 mrb_dir_getwd(mrb_state *mrb, mrb_value klass)
 {
   mrb_value path;
@@ -143,7 +143,7 @@ mrb_dir_getwd(mrb_state *mrb, mrb_value klass)
   return path;
 }
 
-mrb_value
+static mrb_value
 mrb_dir_mkdir(mrb_state *mrb, mrb_value klass)
 {
   mrb_int mode;
@@ -159,7 +159,7 @@ mrb_dir_mkdir(mrb_state *mrb, mrb_value klass)
   return mrb_fixnum_value(0);
 }
 
-mrb_value
+static mrb_value
 mrb_dir_chdir(mrb_state *mrb, mrb_value klass)
 {
   mrb_value spath;
@@ -173,7 +173,7 @@ mrb_dir_chdir(mrb_state *mrb, mrb_value klass)
   return mrb_fixnum_value(0);
 }
 
-mrb_value
+static mrb_value
 mrb_dir_chroot(mrb_state *mrb, mrb_value self)
 {
 #if defined(_WIN32) || defined(_WIN64) || defined(__ANDROID__)
@@ -205,7 +205,7 @@ skip_name_p(const char *name)
   return FALSE;
 }
 
-mrb_value
+static mrb_value
 mrb_dir_empty(mrb_state *mrb, mrb_value self)
 {
   mrb_value path;
@@ -229,7 +229,7 @@ mrb_dir_empty(mrb_state *mrb, mrb_value self)
   return result;
 }
 
-mrb_value
+static mrb_value
 mrb_dir_read(mrb_state *mrb, mrb_value self)
 {
   struct mrb_dir *mdir;
@@ -249,7 +249,7 @@ mrb_dir_read(mrb_state *mrb, mrb_value self)
   }
 }
 
-mrb_value
+static mrb_value
 mrb_dir_rewind(mrb_state *mrb, mrb_value self)
 {
   struct mrb_dir *mdir;
@@ -263,7 +263,7 @@ mrb_dir_rewind(mrb_state *mrb, mrb_value self)
   return self;
 }
 
-mrb_value
+static mrb_value
 mrb_dir_seek(mrb_state *mrb, mrb_value self)
 {
   #if defined(_WIN32) || defined(_WIN64) || defined(__ANDROID__)
@@ -284,7 +284,7 @@ mrb_dir_seek(mrb_state *mrb, mrb_value self)
   #endif
 }
 
-mrb_value
+static mrb_value
 mrb_dir_tell(mrb_state *mrb, mrb_value self)
 {
 #if defined(_WIN32) || defined(_WIN64) || defined(__ANDROID__)