diff --git a/src/bus.rs b/src/bus.rs
index 4a57ddf..fcc7b4f 100644
--- a/src/bus.rs
+++ b/src/bus.rs
@@ -37,7 +37,7 @@ impl Bus {
                     }
                     0x02 => {
                         // we're reading the framebuffer pointer of this overlay
-                        overlay_lock[overlay_number].framebuffer_pointer + 0x02000000
+                        overlay_lock[overlay_number].framebuffer_pointer + 0x80000000
                     }
                     0x03 => {
                         // we're reading the enable status of this overlay
@@ -108,7 +108,7 @@ impl Bus {
                         if word < 0x02000000 {
                             panic!("overlay framebuffer must be within shared memory");
                         }
-                        overlay_lock[overlay_number].framebuffer_pointer = word - 0x02000000;
+                        overlay_lock[overlay_number].framebuffer_pointer = word - 0x80000000;
                     }
                     0x03 => {
                         // we're setting the enable status of this overlay
@@ -121,7 +121,7 @@ impl Bus {
                 if word < 0x02000000 {
                     panic!("audio buffer must be within shared memory");
                 }
-                let address = word as usize - 0x02000000;
+                let address = word as usize - 0x80000000;
                 let shared_memory_lock = self.memory.shared_memory.lock().unwrap();
 
                 let length = u32::from_le_bytes(shared_memory_lock[address..address+4].try_into().unwrap()) as usize;
diff --git a/src/main.rs b/src/main.rs
index 2e97a3c..df53ece 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -61,11 +61,7 @@ fn main() {
     let mouse = Arc::new(Mutex::new(Mouse::new()));
 
     // 32 MiB of shared memory
-    // add some "bonus bytes" at the end of memory to prevent dumb errors - (lua was here)
-    // see the ImmediatePtr match arm in read_source() in cpu.rs for more info
-    // basically all immediate pointers read 32 bits, even if the opcode size is smaller
-    // so attempting to read something like the last byte of shared memory (0x03FFFFFF) would previously panic
-    let shared_memory = Arc::new(Mutex::new(vec![0u8; 0x0200000F]));
+    let shared_memory = Arc::new(Mutex::new(vec![0u8; 0x02000000]));
 
     let mut cpu = {
         // 32 MiB of fast memory
@@ -80,7 +76,7 @@ fn main() {
         println!("Fast memory: {:.2}MB mapped at {:#010X}-{:#010X}", fast_size / 1048576, fast_bottom_address, fast_top_address);
 
         let shared_size = { cpu_shared_memory.lock().unwrap().len() };
-        let shared_bottom_address = 0x02000000;
+        let shared_bottom_address = 0x80000000;
         let shared_top_address = shared_bottom_address + shared_size - 1;
         println!("Shared memory: {:.2}MB mapped at {:#010X}-{:#010X}", shared_size / 1048576, shared_bottom_address, shared_top_address);
 
diff --git a/src/memory.rs b/src/memory.rs
index f1362b3..df21937 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -1,38 +1,56 @@
 // memory.rs
 
-use crate::{Overlay};
+use crate::Overlay;
 
 use std::sync::{Arc, Mutex};
 
 pub struct Memory {
     pub fast_memory: Vec<u8>,
+    fast_memory_size: usize,
     pub shared_memory: Arc<Mutex<Vec<u8>>>,
+    shared_memory_size: usize,
 
     pub overlays: Arc<Mutex<Vec<Overlay>>>,
 
     pub rom: Vec<u8>,
+    rom_size: usize,
 }
 
 impl Memory {
     pub fn new(fast_memory: Vec<u8>, shared_memory: Arc<Mutex<Vec<u8>>>, overlays: Arc<Mutex<Vec<Overlay>>>, rom: Vec<u8>) -> Self {
+        let shared_memory_size = { shared_memory.lock().unwrap().len() };
         Memory {
+            fast_memory_size: fast_memory.len(),
             fast_memory,
+            shared_memory_size,
             shared_memory,
             overlays,
+            rom_size: rom.len(),
             rom,
         }
     }
     pub fn read_8(&self, address: u32) -> u8 {
         let address = address as usize;
-        if address < 0x02000000 {
+
+        let fast_bottom_address = 0x00000000;
+        let fast_top_address = fast_bottom_address + self.fast_memory_size - 1;
+
+        let shared_bottom_address = 0x80000000;
+        let shared_top_address = shared_bottom_address + self.shared_memory_size - 1;
+
+        let rom_bottom_address = 0xF0000000;
+        let rom_top_address = rom_bottom_address + self.rom_size - 1;
+
+        if address >= fast_bottom_address && address <= fast_top_address {
             self.fast_memory[address]
-        } else if address >= 0xF0000000 {
-            let address = address - 0xF0000000;
-            self.rom[address]
-        } else {
-            let address = address - 0x02000000;
+        } else if address >= shared_bottom_address && address <= shared_top_address {
             let shared_memory_lock = self.shared_memory.lock().unwrap();
-            shared_memory_lock[address]
+            shared_memory_lock[address - shared_bottom_address]
+        } else if address >= rom_bottom_address && address <= rom_top_address {
+            self.rom[address - rom_bottom_address]
+        } else {
+            println!("Warning: attempting to read unmapped memory address: {:#010X}", address);
+            0
         }
     }
     pub fn read_16(&self, address: u32) -> u16 {
@@ -40,35 +58,32 @@ impl Memory {
         (self.read_8(address) as u16)
     }
     pub fn read_32(&self, address: u32) -> u32 {
-        let address = address as usize;
-        if address < 0x02000000 {
-            (self.fast_memory[address + 3] as u32) << 24 |
-            (self.fast_memory[address + 2] as u32) << 16 |
-            (self.fast_memory[address + 1] as u32) << 8  |
-            (self.fast_memory[address] as u32)
-        } else if address >= 0xF0000000 {
-            let address = address - 0xF0000000;
-            (self.rom[address + 3] as u32) << 24 |
-            (self.rom[address + 2] as u32) << 16 |
-            (self.rom[address + 1] as u32) << 8  |
-            (self.rom[address] as u32)
-        } else {
-            let address = address - 0x02000000;
-            let shared_memory_lock = self.shared_memory.lock().unwrap();
-            (shared_memory_lock[address + 3] as u32) << 24 |
-            (shared_memory_lock[address + 2] as u32) << 16 |
-            (shared_memory_lock[address + 1] as u32) << 8  |
-            (shared_memory_lock[address] as u32)
-        }
+        (self.read_8(address + 3) as u32) << 24 |
+        (self.read_8(address + 2) as u32) << 16 |
+        (self.read_8(address + 1) as u32) << 8  |
+        (self.read_8(address) as u32)
     }
     pub fn write_8(&mut self, address: u32, byte: u8) {
         let address = address as usize;
-        if address < 0x02000000 {
+
+        let fast_bottom_address = 0x00000000;
+        let fast_top_address = fast_bottom_address + self.fast_memory_size - 1;
+
+        let shared_bottom_address = 0x80000000;
+        let shared_top_address = shared_bottom_address + self.shared_memory_size - 1;
+
+        let rom_bottom_address = 0xF0000000;
+        let rom_top_address = rom_bottom_address + self.rom_size - 1;
+
+        if address >= fast_bottom_address && address <= fast_top_address {
             self.fast_memory[address] = byte;
-        } else {
-            let address = address - 0x02000000;
+        } else if address >= shared_bottom_address && address <= shared_top_address {
             let mut shared_memory_lock = self.shared_memory.lock().unwrap();
-            shared_memory_lock[address] = byte;
+            shared_memory_lock[address - shared_bottom_address] = byte;
+        } else if address >= rom_bottom_address && address <= rom_top_address {
+            println!("Warning: attempting to write to ROM address: {:#010X}", address);
+        } else {
+            println!("Warning: attempting to write to unmapped memory address: {:#010X}", address);
         }
     }
     pub fn write_16(&mut self, address: u32, half: u16) {
@@ -76,19 +91,9 @@ impl Memory {
         self.write_8(address + 1, (half >> 8) as u8);
     }
     pub fn write_32(&mut self, address: u32, word: u32) {
-        let address = address as usize;
-        if address < 0x02000000 {
-            self.fast_memory[address] = (word & 0x000000FF) as u8;
-            self.fast_memory[address + 1] = ((word & 0x0000FF00) >> 8) as u8;
-            self.fast_memory[address + 2] = ((word & 0x00FF0000) >> 16) as u8;
-            self.fast_memory[address + 3] = ((word & 0xFF000000) >> 24) as u8;
-        } else {
-            let address = address - 0x02000000;
-            let mut shared_memory_lock = self.shared_memory.lock().unwrap();
-            shared_memory_lock[address] = (word & 0x000000FF) as u8;
-            shared_memory_lock[address + 1] = ((word & 0x0000FF00) >> 8) as u8;
-            shared_memory_lock[address + 2] = ((word & 0x00FF0000) >> 16) as u8;
-            shared_memory_lock[address + 3] = ((word & 0xFF000000) >> 24) as u8;
-        }
+        self.write_8(address, (word & 0x000000FF) as u8);
+        self.write_8(address + 1, ((word & 0x0000FF00) >> 8) as u8);
+        self.write_8(address + 2, ((word & 0x00FF0000) >> 16) as u8);
+        self.write_8(address + 3, ((word & 0xFF000000) >> 24) as u8);
     }
 }
\ No newline at end of file