diff --git a/src/arm7tdmi/arm/exec.rs b/src/arm7tdmi/arm/exec.rs
index 337e051..a8b2463 100644
--- a/src/arm7tdmi/arm/exec.rs
+++ b/src/arm7tdmi/arm/exec.rs
@@ -381,7 +381,7 @@ impl Core {
                 ArmHalfwordTransferType::UnsignedHalfwords => {
                     self.store_16(addr, value as u16, bus)
                 }
-                _ => panic!("invalid HS flags for L=0")
+                _ => panic!("invalid HS flags for L=0"),
             };
         }
 
diff --git a/src/bin/main.rs b/src/bin/main.rs
index a1c14b2..be79b80 100644
--- a/src/bin/main.rs
+++ b/src/bin/main.rs
@@ -14,13 +14,12 @@ use rustboyadvance_ng::{GBAResult, GameBoyAdvance};
 fn run_debug(matches: &ArgMatches) -> GBAResult<()> {
     let skip_bios = match matches.occurrences_of("skip_bios") {
         0 => false,
-        _ => true
+        _ => true,
     };
 
     let bios_bin = read_bin_file(matches.value_of("bios").unwrap_or_default())?;
-    let rom_bin = read_bin_file(matches.value_of("game_rom").unwrap())?;
 
-    let gamepak = Cartridge::new(rom_bin);
+    let gamepak = Cartridge::load(matches.value_of("game_rom").unwrap())?;
     println!("loaded rom: {:#?}", gamepak.header);
 
     let mut core = Core::new();
diff --git a/src/cartridge.rs b/src/cartridge.rs
index 5b16c60..6c66f4e 100644
--- a/src/cartridge.rs
+++ b/src/cartridge.rs
@@ -5,6 +5,8 @@ use crate::arm7tdmi::{
     Addr,
 };
 use crate::sysbus::WaitState;
+use crate::util::read_bin_file;
+use crate::GBAError;
 
 /// From GBATEK
 ///
@@ -73,13 +75,20 @@ pub struct Cartridge {
 }
 
 impl Cartridge {
-    pub fn new(gamepak: Vec<u8>) -> Cartridge {
-        let header = CartridgeHeader::parse(&gamepak);
-        Cartridge {
-            header: header,
-            bytes: gamepak.into_boxed_slice(),
-            ws: WaitState::new(5, 5, 8),
+    const MIN_SIZE: usize = 4 * 1024 * 1024;
+
+    pub fn load(path: &str) -> Result<Cartridge, GBAError> {
+        let mut rom_bin = read_bin_file(path)?;
+        if rom_bin.len() < Cartridge::MIN_SIZE {
+            rom_bin.resize_with(Cartridge::MIN_SIZE, Default::default);
         }
+
+        let header = CartridgeHeader::parse(&rom_bin);
+        Ok(Cartridge {
+            header: header,
+            bytes: rom_bin.into_boxed_slice(),
+            ws: WaitState::new(5, 5, 8),
+        })
     }
 }