diff --git a/src/error.rs b/src/error.rs
index 6662137..2f5ed81 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -2,7 +2,7 @@ use std::fmt;
 use std::io;
 use yubikey_piv::{key::RetiredSlotId, Serial};
 
-use crate::USABLE_SLOTS;
+use crate::util::slot_to_ui;
 
 pub enum Error {
     CustomManagementKey,
@@ -84,12 +84,12 @@ impl fmt::Debug for Error {
             Error::SlotHasNoIdentity(slot) => writeln!(
                 f,
                 "Slot {} does not contain an age identity or compatible key.",
-                USABLE_SLOTS.iter().position(|s| s == slot).unwrap() + 1
+                slot_to_ui(slot)
             )?,
             Error::SlotIsNotEmpty(slot) => writeln!(
                 f,
                 "Slot {} is not empty. Use --force to overwrite the slot.",
-                USABLE_SLOTS.iter().position(|s| s == slot).unwrap() + 1
+                slot_to_ui(slot)
             )?,
             Error::TimedOut => {
                 writeln!(f, "Timed out while waiting for a YubiKey to be inserted.")?
diff --git a/src/main.rs b/src/main.rs
index e6b9088..16d4027 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -100,15 +100,7 @@ struct PluginOptions {
 
 fn generate(opts: PluginOptions) -> Result<(), Error> {
     let serial = opts.serial.map(|s| s.into());
-    let slot = opts
-        .slot
-        .map(|slot| {
-            USABLE_SLOTS
-                .get(slot as usize - 1)
-                .cloned()
-                .ok_or(Error::InvalidSlot(slot))
-        })
-        .transpose()?;
+    let slot = opts.slot.map(util::ui_to_slot).transpose()?;
     let pin_policy = opts
         .pin_policy
         .map(util::pin_policy_from_string)
@@ -134,15 +126,7 @@ fn generate(opts: PluginOptions) -> Result<(), Error> {
 
 fn identity(opts: PluginOptions) -> Result<(), Error> {
     let serial = opts.serial.map(|s| s.into());
-    let slot = opts
-        .slot
-        .map(|slot| {
-            USABLE_SLOTS
-                .get(slot as usize - 1)
-                .cloned()
-                .ok_or(Error::InvalidSlot(slot))
-        })
-        .transpose()?;
+    let slot = opts.slot.map(util::ui_to_slot).transpose()?;
 
     let mut yubikey = yubikey::open(serial)?;
 
@@ -240,8 +224,7 @@ fn list(all: bool) -> Result<(), Error> {
             println!(
                 "#       Serial: {}, Slot: {}",
                 yubikey.serial(),
-                // Use 1-indexing in the UI for niceness
-                USABLE_SLOTS.iter().position(|s| s == &slot).unwrap() + 1,
+                util::slot_to_ui(&slot),
             );
             println!("#         Name: {}", name);
             println!("#      Created: {}", created);
diff --git a/src/util.rs b/src/util.rs
index 0a027a1..2f7c074 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -1,13 +1,27 @@
 use x509_parser::{certificate::X509Certificate, der_parser::oid::Oid};
 use yubikey_piv::{
+    key::RetiredSlotId,
     policy::{PinPolicy, TouchPolicy},
     Key, YubiKey,
 };
 
-use crate::{error::Error, p256::Recipient, yubikey::Stub, PLUGIN_NAME};
+use crate::{error::Error, p256::Recipient, yubikey::Stub, PLUGIN_NAME, USABLE_SLOTS};
 
 pub(crate) const POLICY_EXTENSION_OID: &[u64] = &[1, 3, 6, 1, 4, 1, 41482, 3, 8];
 
+pub(crate) fn ui_to_slot(slot: u8) -> Result<RetiredSlotId, Error> {
+    // Use 1-indexing in the UI for niceness
+    USABLE_SLOTS
+        .get(slot as usize - 1)
+        .cloned()
+        .ok_or(Error::InvalidSlot(slot))
+}
+
+pub(crate) fn slot_to_ui(slot: &RetiredSlotId) -> u8 {
+    // Use 1-indexing in the UI for niceness
+    USABLE_SLOTS.iter().position(|s| s == slot).unwrap() as u8 + 1
+}
+
 pub(crate) fn pin_policy_from_string(s: String) -> Result<PinPolicy, Error> {
     match s.as_str() {
         "always" => Ok(PinPolicy::Always),