diff --git a/mrbgems/mruby-hash-ext/mrblib/hash.rb b/mrbgems/mruby-hash-ext/mrblib/hash.rb
index 9ba326bc2..97e1031f9 100644
--- a/mrbgems/mruby-hash-ext/mrblib/hash.rb
+++ b/mrbgems/mruby-hash-ext/mrblib/hash.rb
@@ -32,13 +32,9 @@ class Hash
       other = others[i]
       i += 1
       raise TypeError, "Hash required (#{other.class} given)" unless Hash === other
-      if block
-        other.each_key{|k|
-          self[k] = (self.has_key?(k))? block.call(k, self[k], other[k]): other[k]
-        }
-      else
-        other.each_key{|k| self[k] = other[k]}
-      end
+      other.each_key{|k|
+        self[k] = (self.has_key?(k))? block.call(k, self[k], other[k]): other[k]
+      }
     end
     self
   end
diff --git a/mrbgems/mruby-hash-ext/src/hash_ext.c b/mrbgems/mruby-hash-ext/src/hash_ext.c
index 26b042007..5b990d936 100644
--- a/mrbgems/mruby-hash-ext/src/hash_ext.c
+++ b/mrbgems/mruby-hash-ext/src/hash_ext.c
@@ -295,6 +295,44 @@ hash_deconstruct_keys(mrb_state *mrb, mrb_value hash)
   return result;
 }
 
+/*
+ *  call-seq:
+ *     hsh.__merge(*others) -> hsh
+ *
+ *  Merges multiple hashes into hsh. This is an internal method
+ *  used by merge! for non-block cases.
+ *
+ *  Raises ArgumentError if no arguments given.
+ *  Raises TypeError if any argument is not a Hash.
+ *
+ *     h = { a: 1, b: 2 }
+ *     h.__merge({ c: 3 }, { d: 4 })  #=> { a: 1, b: 2, c: 3, d: 4 }
+ */
+static mrb_value
+hash_merge(mrb_state *mrb, mrb_value hash)
+{
+  const mrb_value *argv;
+  mrb_int argc;
+
+  mrb_get_args(mrb, "*", &argv, &argc);
+
+  /* Validate arguments */
+  if (argc == 0) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "wrong number of arguments (given 0, expected 1+)");
+  }
+
+  /* Merge multiple hashes in C */
+  for (mrb_int i = 0; i < argc; i++) {
+    if (!mrb_hash_p(argv[i])) {
+      mrb_raisef(mrb, E_TYPE_ERROR, "no implicit conversion of %C into Hash",
+                 mrb_obj_class(mrb, argv[i]));
+    }
+    mrb_hash_merge(mrb, hash, argv[i]);
+  }
+
+  return hash;
+}
+
 void
 mrb_mruby_hash_ext_gem_init(mrb_state *mrb)
 {
@@ -306,6 +344,7 @@ mrb_mruby_hash_ext_gem_init(mrb_state *mrb)
   mrb_define_method_id(mrb, h, MRB_SYM(except),    hash_except, MRB_ARGS_ANY());
   mrb_define_method_id(mrb, h, MRB_SYM(key),       hash_key, MRB_ARGS_REQ(1));
   mrb_define_method_id(mrb, h, MRB_SYM(deconstruct_keys), hash_deconstruct_keys, MRB_ARGS_REQ(1));
+  mrb_define_method_id(mrb, h, MRB_SYM(__merge),   hash_merge, MRB_ARGS_ANY());
   mrb_define_class_method_id(mrb, h, MRB_OPSYM(aref), hash_s_create, MRB_ARGS_ANY());
 }
 
diff --git a/mrbgems/mruby-hash-ext/test/hash.rb b/mrbgems/mruby-hash-ext/test/hash.rb
index 32d4561d9..30014e946 100644
--- a/mrbgems/mruby-hash-ext/test/hash.rb
+++ b/mrbgems/mruby-hash-ext/test/hash.rb
@@ -46,27 +46,27 @@ assert('Hash.[] for sub class') do
 end
 
 assert('Hash#merge!') do
+  # Single hash merge
   a = { 'abc_key' => 'abc_value', 'cba_key' => 'cba_value' }
   b = { 'cba_key' => 'XXX', 'xyz_key' => 'xyz_value' }
-
   result_1 = a.merge! b
+  assert_equal({'abc_key' => 'abc_value', 'cba_key' => 'XXX',
+               'xyz_key' => 'xyz_value' }, result_1)
 
+  # Block handling
   a = { 'abc_key' => 'abc_value', 'cba_key' => 'cba_value' }
   result_2 = a.merge!(b) do |key, original, new|
     original
   end
-
-  assert_equal({'abc_key' => 'abc_value', 'cba_key' => 'XXX',
-               'xyz_key' => 'xyz_value' }, result_1)
   assert_equal({'abc_key' => 'abc_value', 'cba_key' => 'cba_value',
                'xyz_key' => 'xyz_value' }, result_2)
 
-  assert_raise(TypeError) do
-    { 'abc_key' => 'abc_value' }.merge! "a"
-  end
-
-  # multiple arguments
+  # Multiple arguments
   assert_equal({a:1,b:2,c:3}, {a:1}.merge!({b:2},{c:3}))
+
+  # Error cases
+  assert_raise(ArgumentError) { {}.merge!() }
+  assert_raise(TypeError) { {}.merge!("not a hash") }
 end
 
 assert('Hash#values_at') do