diff --git a/package-lock.json b/package-lock.json
index 3c85777..d24cfad 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11,6 +11,7 @@
         "@otplib/core": "^12.0.1",
         "@otplib/plugin-crypto-js": "^12.0.1",
         "@popperjs/core": "^2.11.8",
+        "base32-decode": "^1.0.0",
         "bootstrap": "^5.3.3",
         "classnames": "^2.5.1",
         "react": "^18.2.0",
@@ -1930,6 +1931,12 @@
       "integrity": "sha512-3oSeUO0TMV67hN1AmbXsK4yaqU7tjiHlbxRDZOpH0KW9+CeX4bRAaX0Anxt0tx2MrpRpWwQaPwIlISEJhYU5Pw==",
       "dev": true
     },
+    "node_modules/base32-decode": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/base32-decode/-/base32-decode-1.0.0.tgz",
+      "integrity": "sha512-KNWUX/R7wKenwE/G/qFMzGScOgVntOmbE27vvc6GrniDGYb6a5+qWcuoXl8WIOQL7q0TpK7nZDm1Y04Yi3Yn5g==",
+      "license": "MIT"
+    },
     "node_modules/base64-js": {
       "version": "1.5.1",
       "resolved": "https://registry.npmjs.org/base64-js/-/base64-js-1.5.1.tgz",
diff --git a/package.json b/package.json
index a908006..fea854f 100644
--- a/package.json
+++ b/package.json
@@ -13,6 +13,7 @@
     "@otplib/core": "^12.0.1",
     "@otplib/plugin-crypto-js": "^12.0.1",
     "@popperjs/core": "^2.11.8",
+    "base32-decode": "^1.0.0",
     "bootstrap": "^5.3.3",
     "classnames": "^2.5.1",
     "react": "^18.2.0",
diff --git a/src/App.tsx b/src/App.tsx
index 0af46ad..9512da5 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -1,10 +1,12 @@
 import React, {useState} from 'react';
+import base32Decode from 'base32-decode';
 import {NumberInput, TextInput} from './Input';
-import OTPOutput, {HashAlgorithm} from './OTPOutput';
+import OTPOutput from './OTPOutput';
 import Select from './Select';
 import Collapsible from './Collapsible';
 import ActionLink from './ActionLink';
 import {type State, defaults, serializeState, deserializeState} from './state';
+import {HashAlgorithm} from './algorithms.tsx';
 
 function parseState() {
   if (window.location.hash.startsWith('#!')) {
@@ -20,9 +22,17 @@ function App() {
   const {secret, step, digits, algorithm} = state;
   const [offset, setOffset] = React.useState(0);
 
+  const [validSecret, decoded] = React.useMemo(() => {
+    try {
+      return [true, base32Decode(secret.toUpperCase(), 'RFC4648')];
+    } catch (e) {
+      return [false, undefined];
+    }
+  }, [secret]);
+
   const validStep = step > 0;
   const validDigits = digits > 0 && digits <= 10;
-  const valid = validStep && validDigits && !!secret;
+  const valid = validSecret && validStep && validDigits && !!secret;
 
   React.useEffect(() => {
     if (!validStep) return;
@@ -74,7 +84,6 @@ function App() {
 
   React.useEffect(() => {
     const value = serializeState(state);
-    console.log(value);
     history.replaceState(null, '', window.location.pathname + window.location.search + (value && `#!${value}`));
   }, [state]);
 
@@ -91,7 +100,8 @@ function App() {
   return (
     <div className="totp-app">
       <div className="totp-settings">
-        <TextInput label="Secret key" value={secret} onChange={setSecret}/>
+        <TextInput label="Secret key" value={secret} onChange={setSecret}
+                   error={!validSecret && 'Secret must be a valid base32-encoded string'}/>
         {advanced ?
           <ActionLink onClick={hideAdvanced}>Hide advanced options</ActionLink> :
           <ActionLink onClick={showAdvanced}>Show advanced options</ActionLink>}
@@ -108,7 +118,7 @@ function App() {
           <button type="button" className="btn btn-secondary" onClick={onReset}>Reset</button>
         </Collapsible>
       </div>
-      {valid && <OTPOutput secret={secret} offset={offset} algorithm={algorithm} digits={digits}/>}
+      {valid && <OTPOutput secret={decoded} offset={offset} algorithm={algorithm} digits={digits}/>}
     </div>
   );
 }
diff --git a/src/OTPOutput.tsx b/src/OTPOutput.tsx
index 1739433..9206a2a 100644
--- a/src/OTPOutput.tsx
+++ b/src/OTPOutput.tsx
@@ -1,16 +1,9 @@
 import React from 'react';
-import {HashAlgorithms, HOTP, HOTPOptions} from '@otplib/core';
+import {HOTP, HOTPOptions} from '@otplib/core';
 import {createDigest} from '@otplib/plugin-crypto-js';
 import classNames from 'classnames';
 import CopyButton from './CopyButton.tsx';
-
-export const ALGORITHMS = {
-  sha1: HashAlgorithms.SHA1,
-  sha256: HashAlgorithms.SHA256,
-  sha512: HashAlgorithms.SHA512,
-};
-
-export type HashAlgorithm = keyof typeof ALGORITHMS;
+import {ALGORITHMS, HashAlgorithm} from './algorithms.tsx';
 
 function OTPCode({code, delta}: { code: string; delta: number }) {
   return <div className={classNames('totp-code', {
diff --git a/src/algorithms.tsx b/src/algorithms.tsx
new file mode 100644
index 0000000..ec594bc
--- /dev/null
+++ b/src/algorithms.tsx
@@ -0,0 +1,9 @@
+import {HashAlgorithms} from '@otplib/core';
+
+export const ALGORITHMS = {
+  sha1: HashAlgorithms.SHA1,
+  sha256: HashAlgorithms.SHA256,
+  sha512: HashAlgorithms.SHA512,
+};
+
+export type HashAlgorithm = keyof typeof ALGORITHMS;
diff --git a/src/state.tsx b/src/state.tsx
index 3cd8e2e..f2e5f39 100644
--- a/src/state.tsx
+++ b/src/state.tsx
@@ -1,4 +1,5 @@
-import {ALGORITHMS, HashAlgorithm} from './OTPOutput';
+
+import {ALGORITHMS, HashAlgorithm} from './algorithms.tsx';
 
 export type State = {
   secret: string;