diff --git a/src/mrb_ext.c b/src/mrb_ext.c
index 93aa3d9..0e4c320 100644
--- a/src/mrb_ext.c
+++ b/src/mrb_ext.c
@@ -126,8 +126,10 @@ void mrb_ext_set_instance_tt(struct RClass* class, enum mrb_vtype type) {
   MRB_SET_INSTANCE_TT(class, type);
 }
 
-int mrb_ext_ary_len(struct mrb_state* mrb, mrb_value array) {
-  return mrb_ary_len(mrb, array);
+long long mrb_ext_ary_len(struct mrb_state* mrb, mrb_value array) {
+  (void)mrb;
+  mrb_assert(mrb_array_p(array));
+  return RARRAY_LEN(array);
 }
 
 unsigned int mrb_ext_get_mid(struct mrb_state* mrb) {
diff --git a/src/mruby/get_mruby.sh b/src/mruby/get_mruby.sh
index 43b35c1..616bff5 100755
--- a/src/mruby/get_mruby.sh
+++ b/src/mruby/get_mruby.sh
@@ -14,8 +14,9 @@
 # * compile, linker & archiver
 # * unzip
 
-VERSION=1.2.0
+VERSION=1.4.1
 CURRENT=$PWD
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null && pwd )"
 
 # Checks is /tmp/mruby needs cleaning or creation.
 
@@ -35,6 +36,9 @@ mkdir -p mruby-out/src/mrbgems
 
 cd mruby-$VERSION
 
+# Use only supported gems.
+cat $DIR/mrusty.gembox > mrbgems/default.gembox
+
 # minirake compiles the compiler and rb files to C.
 
 ./minirake
@@ -64,11 +68,30 @@ rm -rf build/host/mrbgems/mruby-bin*
 rm -rf mrbgems/mruby-test
 rm -rf build/host/mrbgems/mruby-test
 
+rm -rf mrbgems/mruby-io*
+rm -rf build/host/mrbgems/mruby-io*
+
+rm -rf mrbgems/mruby-socket*
+rm -rf build/host/mrbgems/mruby-socket*
+
 # Copies all gems.
 
 cp -R mrbgems/* ../mruby-out/src/mrbgems
 cp -R build/host/mrbgems/* ../mruby-out/src/mrbgems
 
+# String needs additional mruby header.
+
+sed -i -e $'s/#include "common.h"/#include "mruby.h"\\\n#include "common.h"/g' include/mruby/string.h
+
+# Copies header files so they will be available in top level includes.
+
+find include/mruby -type f -name '*.h' -exec cp {} ../mruby-out/include \;
+
+# Copies ext header files required by gems.
+
+mkdir -p ../mruby-out/include/mruby/ext
+find mrbgems -path '*/ext/*' -name '*.h' -exec cp {} ../mruby-out/include/mruby/ext \;
+
 cd ..
 
 tar -cf $CURRENT/mruby-out.tar mruby-out
diff --git a/src/mruby/mruby-out.tar b/src/mruby/mruby-out.tar
index 032a0c9..467a631 100644
Binary files a/src/mruby/mruby-out.tar and b/src/mruby/mruby-out.tar differ
diff --git a/src/mruby/mrusty.gembox b/src/mruby/mrusty.gembox
new file mode 100644
index 0000000..1073873
--- /dev/null
+++ b/src/mruby/mrusty.gembox
@@ -0,0 +1,88 @@
+MRuby::GemBox.new do |conf|
+  # Use standard IO/File class
+  # conf.gem :core => "mruby-io"
+
+  # Use standard Array#pack, String#unpack methods
+  conf.gem :core => "mruby-pack"
+
+  # Use standard Kernel#sprintf method
+  conf.gem :core => "mruby-sprintf"
+
+  # Use standard print/puts/p
+  conf.gem :core => "mruby-print"
+
+  # Use standard Math module
+  conf.gem :core => "mruby-math"
+
+  # Use standard Time class
+  conf.gem :core => "mruby-time"
+
+  # Use standard Struct class
+  conf.gem :core => "mruby-struct"
+
+  # Use Comparable module extension
+  conf.gem :core => "mruby-compar-ext"
+
+  # Use Enumerable module extension
+  conf.gem :core => "mruby-enum-ext"
+
+  # Use String class extension
+  conf.gem :core => "mruby-string-ext"
+
+  # Use Numeric class extension
+  conf.gem :core => "mruby-numeric-ext"
+
+  # Use Array class extension
+  conf.gem :core => "mruby-array-ext"
+
+  # Use Hash class extension
+  conf.gem :core => "mruby-hash-ext"
+
+  # Use Range class extension
+  conf.gem :core => "mruby-range-ext"
+
+  # Use Proc class extension
+  conf.gem :core => "mruby-proc-ext"
+
+  # Use Symbol class extension
+  conf.gem :core => "mruby-symbol-ext"
+
+  # Use Random class
+  conf.gem :core => "mruby-random"
+
+  # Use Object class extension
+  conf.gem :core => "mruby-object-ext"
+
+  # Use ObjectSpace class
+  conf.gem :core => "mruby-objectspace"
+
+  # Use Fiber class
+  conf.gem :core => "mruby-fiber"
+
+  # Use Enumerator class (require mruby-fiber)
+  conf.gem :core => "mruby-enumerator"
+
+  # Use Enumerator::Lazy class (require mruby-enumerator)
+  conf.gem :core => "mruby-enum-lazy"
+
+  # Use toplevel object (main) methods extension
+  conf.gem :core => "mruby-toplevel-ext"
+
+  # Generate mirb command
+  # conf.gem :core => "mruby-bin-mirb"
+
+  # Generate mruby command
+  # conf.gem :core => "mruby-bin-mruby"
+
+  # Generate mruby-strip command
+  # conf.gem :core => "mruby-bin-strip"
+
+  # Use Kernel module extension
+  conf.gem :core => "mruby-kernel-ext"
+
+  # Use class/module extension
+  conf.gem :core => "mruby-class-ext"
+
+  # Use mruby-compiler to build other mrbgems
+  conf.gem :core => "mruby-compiler"
+end
diff --git a/src/mruby_ffi.rs b/src/mruby_ffi.rs
index 31fab80..68a2d71 100644
--- a/src/mruby_ffi.rs
+++ b/src/mruby_ffi.rs
@@ -366,7 +366,7 @@ extern "C" {
     #[inline]
     pub fn mrb_ary_set(mrb: *const MrState, array: MrValue, i: i32, value: MrValue);
     #[inline]
-    pub fn mrb_ext_ary_len(mrb: *const MrState, array: MrValue) -> i32;
+    pub fn mrb_ext_ary_len(mrb: *const MrState, array: MrValue) -> i64;
 
     #[inline]
     pub fn mrb_ext_raise(mrb: *const MrState, eclass: *const c_char, msg: *const c_char);