diff --git a/lib/rubyboy/cartridge/mbc1.rb b/lib/rubyboy/cartridge/mbc1.rb
index 833eeee..47c0e09 100644
--- a/lib/rubyboy/cartridge/mbc1.rb
+++ b/lib/rubyboy/cartridge/mbc1.rb
@@ -18,13 +18,13 @@ def initialize(rom, ram)
       end
 
       def set_methods
-        0xc000.times do |addr|
-          @read_methods[addr] =
-            case addr
-            when 0x0000..0x3fff then -> { @rom.data[addr] }
-            when 0x4000..0x7fff then -> { @rom.data[addr + (@rom_bank - 1) * 0x4000] }
-            when 0xa000..0xbfff
-              lambda do
+        0xc.times do |prefix|
+          @read_methods[prefix] =
+            case prefix
+            when 0x0..0x3 then ->(addr) { @rom.data[addr] }
+            when 0x4..0x7 then ->(addr) { @rom.data[addr + (@rom_bank - 1) * 0x4000] }
+            when 0xa..0xb
+              lambda do |addr|
                 if @ram_enable
                   if @ram_banking_mode
                     @ram.eram[addr - 0xa000 + @ram_bank * 0x800]
@@ -38,19 +38,19 @@ def set_methods
             end
         end
 
-        0xc000.times do |addr|
-          @write_methods[addr] =
-            case addr
-            when 0x0000..0x1fff then ->(value) { @ram_enable = value & 0x0f == 0x0a }
-            when 0x2000..0x3fff
-              lambda do |value|
+        0xc.times do |prefix|
+          @write_methods[prefix] =
+            case prefix
+            when 0x0..0x1 then ->(_addr, value) { @ram_enable = value & 0x0f == 0x0a }
+            when 0x2..0x3
+              lambda do |_addr, value|
                 @rom_bank = value & 0x1f
                 @rom_bank = 1 if @rom_bank == 0
               end
-            when 0x4000..0x5fff then ->(value) { @ram_bank = value & 0x03 }
-            when 0x6000..0x7fff then ->(value) { @ram_banking_mode = value & 0x01 == 0x01 }
-            when 0xa000..0xbfff
-              lambda do |value|
+            when 0x4..0x5 then ->(_addr, value) { @ram_bank = value & 0x03 }
+            when 0x6..0x7 then ->(_addr, value) { @ram_banking_mode = value & 0x01 == 0x01 }
+            when 0xa..0xb
+              lambda do |addr, value|
                 if @ram_enable
                   if @ram_banking_mode
                     @ram.eram[addr - 0xa000 + @ram_bank * 0x800] = value
@@ -64,11 +64,11 @@ def set_methods
       end
 
       def read_byte(addr)
-        @read_methods[addr].call
+        @read_methods[addr >> 12].call(addr)
       end
 
       def write_byte(addr, value)
-        @write_methods[addr].call(value)
+        @write_methods[addr >> 12].call(addr, value)
       end
     end
   end