diff --git a/rom/build.rs b/rom/build.rs
index cf5456c..807ecf5 100644
--- a/rom/build.rs
+++ b/rom/build.rs
@@ -13,15 +13,58 @@
 // You should have received a copy of the GNU Affero General Public License
 // along with this program. If not, see <https://www.gnu.org/licenses/>.
 
-use std::fs::File;
+use std::env;
+use std::fmt;
+use std::fs::{self, File};
 use std::io::{BufWriter, Write};
+use std::error::Error as StdError;
 use std::path::Path;
 
 use quote::{format_ident, quote};
 
-fn main() {
+#[derive(Debug, Eq, PartialEq)]
+pub enum Error {
+    EnvVariableError(env::VarError),
+    ROMDoesntExist,
+    UnableToOpenROM,
+}
+
+impl StdError for Error {}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        match self {
+            Error::EnvVariableError(e) => write!(f, "POKEMON_ROM env var error: {}", e),
+            Error::ROMDoesntExist => write!(f, "ROM doesn't exist"),
+            Error::UnableToOpenROM => write!(f, "Unable to open ROM"),
+        }
+    }
+}
+
+impl From<env::VarError> for Error {
+    fn from(err: env::VarError) -> Error {
+        Error::EnvVariableError(err)
+    }
+}
+
+fn get_rom() -> Result<Vec<u8>, Error> {
+    let env_romp = env::var("POKEMON_ROM")?;
+    let romp = Path::new(&env_romp);
+
+    if ! romp.exists() {
+        return Err(Error::ROMDoesntExist);
+    }
+
+    Ok(match fs::read(romp) {
+        Ok(v) => v,
+        Err(_) => return Err(Error::UnableToOpenROM),
+    })
+}
+
+fn main() -> Result<(), Error> {
     let output = Path::new(&env::var("OUT_DIR").unwrap()).join("output.rs");
     let mut output = BufWriter::new(File::create(&output).unwrap());
+    let _rom: Vec<u8> = get_rom()?;
 
     let pkmn_names: Vec<_> = [
         "Rhydon",
@@ -40,4 +83,5 @@ fn main() {
     };
 
     write!(output, "{}", tokens).unwrap();
+    Ok(())
 }