diff --git a/src/jwe/flattened/decrypt.ts b/src/jwe/flattened/decrypt.ts
index 109847a3aa..f2cc02d8e3 100644
--- a/src/jwe/flattened/decrypt.ts
+++ b/src/jwe/flattened/decrypt.ts
@@ -179,7 +179,11 @@ export async function flattenedDecrypt(
 
   let encryptedKey!: Uint8Array
   if (jwe.encrypted_key !== undefined) {
-    encryptedKey = base64url(jwe.encrypted_key!)
+    try {
+      encryptedKey = base64url(jwe.encrypted_key!)
+    } catch {
+      throw new JWEInvalid('Failed to base64url decode the encrypted_key')
+    }
   }
 
   let resolvedKey = false
@@ -205,8 +209,18 @@ export async function flattenedDecrypt(
     cek = generateCek(enc)
   }
 
-  const iv = base64url(jwe.iv)
-  const tag = base64url(jwe.tag)
+  let iv: Uint8Array
+  let tag: Uint8Array
+  try {
+    iv = base64url(jwe.iv)
+  } catch {
+    throw new JWEInvalid('Failed to base64url decode the iv')
+  }
+  try {
+    tag = base64url(jwe.tag)
+  } catch {
+    throw new JWEInvalid('Failed to base64url decode the tag')
+  }
 
   const protectedHeader: Uint8Array = encoder.encode(jwe.protected ?? '')
   let additionalData: Uint8Array
@@ -217,7 +231,13 @@ export async function flattenedDecrypt(
     additionalData = protectedHeader
   }
 
-  let plaintext = await decrypt(enc, cek, base64url(jwe.ciphertext), iv, tag, additionalData)
+  let ciphertext: Uint8Array
+  try {
+    ciphertext = base64url(jwe.ciphertext)
+  } catch {
+    throw new JWEInvalid('Failed to base64url decode the ciphertext')
+  }
+  let plaintext = await decrypt(enc, cek, ciphertext, iv, tag, additionalData)
 
   if (joseHeader.zip === 'DEF') {
     plaintext = await (options?.inflateRaw || inflate)(plaintext)
@@ -230,7 +250,11 @@ export async function flattenedDecrypt(
   }
 
   if (jwe.aad !== undefined) {
-    result.additionalAuthenticatedData = base64url(jwe.aad!)
+    try {
+      result.additionalAuthenticatedData = base64url(jwe.aad!)
+    } catch {
+      throw new JWEInvalid('Failed to base64url decode the aad')
+    }
   }
 
   if (jwe.unprotected !== undefined) {
diff --git a/src/jws/flattened/verify.ts b/src/jws/flattened/verify.ts
index 19fbd34487..4477616891 100644
--- a/src/jws/flattened/verify.ts
+++ b/src/jws/flattened/verify.ts
@@ -173,7 +173,7 @@ export async function flattenedVerify(
   try {
     signature = base64url(jws.signature)
   } catch {
-    throw new JWSInvalid('Failed to parse the base64url encoded signature')
+    throw new JWSInvalid('Failed to base64url decode the signature')
   }
   const verified = await verify(alg, key, signature, data)
 
@@ -183,7 +183,11 @@ export async function flattenedVerify(
 
   let payload: Uint8Array
   if (b64) {
-    payload = base64url(jws.payload)
+    try {
+      payload = base64url(jws.payload)
+    } catch {
+      throw new JWSInvalid('Failed to base64url decode the payload')
+    }
   } else if (typeof jws.payload === 'string') {
     payload = encoder.encode(jws.payload)
   } else {
diff --git a/src/lib/decrypt_key_management.ts b/src/lib/decrypt_key_management.ts
index 7279306559..404295e3e7 100644
--- a/src/lib/decrypt_key_management.ts
+++ b/src/lib/decrypt_key_management.ts
@@ -53,13 +53,21 @@ async function decryptKeyManagement(
       if (joseHeader.apu !== undefined) {
         if (typeof joseHeader.apu !== 'string')
           throw new JWEInvalid(`JOSE Header "apu" (Agreement PartyUInfo) invalid`)
-        partyUInfo = base64url(joseHeader.apu)
+        try {
+          partyUInfo = base64url(joseHeader.apu)
+        } catch {
+          throw new JWEInvalid('Failed to base64url decode the apu')
+        }
       }
 
       if (joseHeader.apv !== undefined) {
         if (typeof joseHeader.apv !== 'string')
           throw new JWEInvalid(`JOSE Header "apv" (Agreement PartyVInfo) invalid`)
-        partyVInfo = base64url(joseHeader.apv)
+        try {
+          partyVInfo = base64url(joseHeader.apv)
+        } catch {
+          throw new JWEInvalid('Failed to base64url decode the apv')
+        }
       }
 
       const sharedSecret = await ECDH.deriveKey(
@@ -105,7 +113,13 @@ async function decryptKeyManagement(
       if (typeof joseHeader.p2s !== 'string')
         throw new JWEInvalid(`JOSE Header "p2s" (PBES2 Salt) missing or invalid`)
 
-      return pbes2Kw(alg, key, encryptedKey, joseHeader.p2c, base64url(joseHeader.p2s))
+      let p2s: Uint8Array
+      try {
+        p2s = base64url(joseHeader.p2s)
+      } catch {
+        throw new JWEInvalid('Failed to base64url decode the p2s')
+      }
+      return pbes2Kw(alg, key, encryptedKey, joseHeader.p2c, p2s)
     }
     case 'A128KW':
     case 'A192KW':
@@ -127,8 +141,18 @@ async function decryptKeyManagement(
       if (typeof joseHeader.tag !== 'string')
         throw new JWEInvalid(`JOSE Header "tag" (Authentication Tag) missing or invalid`)
 
-      const iv = base64url(joseHeader.iv)
-      const tag = base64url(joseHeader.tag)
+      let iv: Uint8Array
+      try {
+        iv = base64url(joseHeader.iv)
+      } catch {
+        throw new JWEInvalid('Failed to base64url decode the iv')
+      }
+      let tag: Uint8Array
+      try {
+        tag = base64url(joseHeader.tag)
+      } catch {
+        throw new JWEInvalid('Failed to base64url decode the tag')
+      }
 
       return aesGcmKw(alg, key, encryptedKey, iv, tag)
     }
diff --git a/src/runtime/browser/asn1.ts b/src/runtime/browser/asn1.ts
index 84152a819f..342f822909 100644
--- a/src/runtime/browser/asn1.ts
+++ b/src/runtime/browser/asn1.ts
@@ -243,7 +243,7 @@ export const fromX509: PEMImportFunction = (pem, alg, options?) => {
     spki = getSPKI(pem)
   } catch (cause) {
     // @ts-ignore
-    throw new TypeError('failed to parse the X.509 certificate', { cause })
+    throw new TypeError('Failed to parse the X.509 certificate', { cause })
   }
   return fromSPKI(spki, alg, options)
 }
diff --git a/src/util/decode_jwt.ts b/src/util/decode_jwt.ts
index b313900d9c..bbbafe7500 100644
--- a/src/util/decode_jwt.ts
+++ b/src/util/decode_jwt.ts
@@ -33,7 +33,7 @@ export function decodeJwt(jwt: string) {
   try {
     decoded = base64url(payload)
   } catch {
-    throw new JWTInvalid('Failed to parse the base64url encoded payload')
+    throw new JWTInvalid('Failed to base64url decode the payload')
   }
 
   let result: unknown