diff --git a/gb-emu/src/main.rs b/gb-emu/src/main.rs
index c5476c8..dcec1c9 100644
--- a/gb-emu/src/main.rs
+++ b/gb-emu/src/main.rs
@@ -40,7 +40,7 @@ struct Args {
     bootrom: Option<String>,
 
     /// Connect the serial port output to stdout
-    #[arg(short, long)]
+    #[arg(long)]
     connect_serial: bool,
 
     /// Show cycle count
@@ -62,6 +62,10 @@ struct Args {
     /// Run debug console
     #[arg(short, long)]
     debug: bool,
+
+    /// Force CGB mode
+    #[arg(short, long)]
+    cgb: bool,
 }
 
 fn main() {
@@ -109,7 +113,8 @@ fn main() {
     })
     .with_bootrom(args.bootrom.map(RomFile::Path))
     .with_no_save(args.no_save)
-    .with_tile_window(tile_window);
+    .with_tile_window(tile_window)
+    .with_cgb_mode(args.cgb);
 
     let mut core = EmulatorCore::init(receiver, options);
 
diff --git a/lib/src/connect/mod.rs b/lib/src/connect/mod.rs
index 7c48c4e..e76b7fc 100644
--- a/lib/src/connect/mod.rs
+++ b/lib/src/connect/mod.rs
@@ -166,6 +166,7 @@ where
     pub(crate) no_save: bool,
     pub(crate) bootrom: Option<RomFile>,
     pub(crate) serial_target: SerialTarget,
+    pub(crate) cgb_mode: bool,
     spooky: PhantomData<ColourFormat>,
 }
 
@@ -185,6 +186,7 @@ where
             no_save: false,
             bootrom: None,
             serial_target: SerialTarget::None,
+            cgb_mode: false,
             spooky: PhantomData,
         }
     }
@@ -207,6 +209,7 @@ where
             no_save: false,
             bootrom: None,
             serial_target: SerialTarget::None,
+            cgb_mode: false,
             spooky: PhantomData,
         }
     }
@@ -245,4 +248,9 @@ where
         self.tile_window = window;
         self
     }
+
+    pub fn with_cgb_mode(mut self, cgb_mode: bool) -> Self {
+        self.cgb_mode = cgb_mode;
+        self
+    }
 }
diff --git a/lib/src/constants.rs b/lib/src/constants.rs
index 6b29e1d..3c4d28d 100644
--- a/lib/src/constants.rs
+++ b/lib/src/constants.rs
@@ -1,7 +1,10 @@
-use crate::processor::memory::rom::CgbRomType;
 use once_cell::sync::OnceCell;
 
 // Hz
 pub const CLOCK_SPEED: usize = 4194304;
 
-pub(crate) static IS_CGB: OnceCell<CgbRomType> = OnceCell::new();
+pub(crate) static STATIC_IS_CGB: OnceCell<bool> = OnceCell::new();
+
+pub(crate) fn is_cgb() -> bool {
+    STATIC_IS_CGB.get().copied().unwrap_or(false)
+}
diff --git a/lib/src/lib.rs b/lib/src/lib.rs
index 3b94f9f..fa01c19 100644
--- a/lib/src/lib.rs
+++ b/lib/src/lib.rs
@@ -8,8 +8,9 @@ use connect::{
     AudioOutput, CameraWrapper, CameraWrapperRef, EmulatorMessage, EmulatorOptions, NoCamera,
     PocketCamera, Renderer, RomFile, SerialTarget,
 };
+use constants::{is_cgb, STATIC_IS_CGB};
 use processor::{
-    memory::{mmio::gpu::Colour, Rom},
+    memory::{mmio::gpu::Colour, rom::CgbRomType, Rom},
     Cpu, CpuSaveState,
 };
 use std::{
@@ -76,10 +77,15 @@ where
             RomFile::Raw(data) => Rom::load(data, None, camera.clone()),
         };
 
+        let _ = STATIC_IS_CGB.set(rom.rom_type == CgbRomType::CgbOnly || options.cgb_mode);
+
         options.window.prepare(WIDTH, HEIGHT);
-        options
-            .window
-            .set_title(format!("{} on {}", rom.get_title(), rom.mbc_type()));
+        options.window.set_title(format!(
+            "{} on {} on {}",
+            rom.get_title(),
+            rom.mbc_type(),
+            if is_cgb() { "CGB" } else { "DMG" }
+        ));
 
         let bootrom_enabled = options.bootrom.is_some();
         let bootrom: Option<Vec<u8>> = options.bootrom.map(|v| match v {
diff --git a/lib/src/processor/memory.rs b/lib/src/processor/memory.rs
index ee4fb14..365d9c7 100644
--- a/lib/src/processor/memory.rs
+++ b/lib/src/processor/memory.rs
@@ -11,6 +11,7 @@ use self::{
 };
 use crate::{
     connect::{AudioOutput, CameraWrapperRef, JoypadState, PocketCamera, Renderer, SerialTarget},
+    constants::is_cgb,
     Cpu,
 };
 
@@ -243,7 +244,13 @@ where
                 0xFF4B => self.gpu.get_wx(),
                 0x0..0xFF40 | 0xFF4C..=0xFFFF => unreachable!(),
             },
-            IoAddress::Cgb(_) => todo!(),
+            IoAddress::Cgb(_) => {
+                if is_cgb() {
+                    todo!();
+                } else {
+                    0xFF
+                }
+            }
             IoAddress::Unused(_) => 0xFF,
         }
     }
@@ -283,7 +290,11 @@ where
                 0xFF4B => self.gpu.update_wx(data),
                 0x0..0xFF40 | 0xFF4C..=0xFFFF => unreachable!(),
             },
-            IoAddress::Cgb(_) => todo!(),
+            IoAddress::Cgb(_) => {
+                if is_cgb() {
+                    todo!()
+                }
+            }
             IoAddress::Unused(_) => {}
         }
     }
diff --git a/lib/src/processor/memory/rom.rs b/lib/src/processor/memory/rom.rs
index b9284a9..44e50c5 100644
--- a/lib/src/processor/memory/rom.rs
+++ b/lib/src/processor/memory/rom.rs
@@ -1,9 +1,5 @@
+use crate::connect::{CameraWrapperRef, PocketCamera as PocketCameraTrait};
 use serde::{Deserialize, Serialize};
-
-use crate::{
-    connect::{CameraWrapperRef, PocketCamera as PocketCameraTrait},
-    constants::IS_CGB,
-};
 use std::{
     fs::{File, OpenOptions},
     io::{Read, Seek, SeekFrom, Write},
@@ -127,7 +123,7 @@ impl Drop for MaybeBufferedSram {
     }
 }
 
-#[derive(Serialize, Deserialize)]
+#[derive(Serialize, Deserialize, Debug, PartialEq)]
 pub(crate) enum CgbRomType {
     Dmg,
     CgbOptional,
@@ -140,6 +136,7 @@ where
 {
     title: String,
     mbc: Box<dyn Mbc>,
+    pub(crate) rom_type: CgbRomType,
     spooky: PhantomData<C>,
 }
 
@@ -207,7 +204,7 @@ where
             .expect("Error parsing title")
             .to_string();
 
-        let _ = IS_CGB.set(get_cgb_rom_type(data[0x143]));
+        let rom_type = get_cgb_rom_type(data[0x143]);
 
         let _sgb_flag = data[0x146];
         let rom_size = data[0x148];
@@ -238,6 +235,7 @@ where
         Self {
             title,
             mbc,
+            rom_type,
             spooky: PhantomData,
         }
     }
@@ -247,10 +245,11 @@ where
         data: Vec<u8>,
         camera: CameraWrapperRef<C>,
     ) -> Self {
-        let _ = IS_CGB.set(get_cgb_rom_type(data[0x143]));
+        let rom_type = get_cgb_rom_type(data[0x143]);
         Self {
             title: state.title,
             mbc: state.mbc.get_mbc(data, camera),
+            rom_type,
             spooky: PhantomData,
         }
     }