diff --git a/ext/web/00_infra.js b/ext/web/00_infra.js
index a250dd69b93e59..64d40f9db4e16b 100644
--- a/ext/web/00_infra.js
+++ b/ext/web/00_infra.js
@@ -233,7 +233,7 @@
   }
 
   /**
-   * @param {Uint8Array} data
+   * @param {string} data
    * @returns {string}
    */
   function forgivingBase64Encode(data) {
@@ -242,7 +242,7 @@
 
   /**
    * @param {string} data
-   * @returns {Uint8Array}
+   * @returns {string}
    */
   function forgivingBase64Decode(data) {
     return core.opSync("op_base64_decode", data);
diff --git a/ext/web/05_base64.js b/ext/web/05_base64.js
index 1244ecfd5cf36b..388c0a5827ce80 100644
--- a/ext/web/05_base64.js
+++ b/ext/web/05_base64.js
@@ -37,12 +37,7 @@
       context: "Argument 1",
     });
 
-    const uint8Array = forgivingBase64Decode(data);
-    const result = ArrayPrototypeMap(
-      [...new SafeArrayIterator(uint8Array)],
-      (byte) => StringFromCharCode(byte),
-    );
-    return ArrayPrototypeJoin(result, "");
+    return forgivingBase64Decode(data);
   }
 
   /**
@@ -56,20 +51,7 @@
       prefix,
       context: "Argument 1",
     });
-    const byteArray = ArrayPrototypeMap(
-      [...new SafeArrayIterator(data)],
-      (char) => {
-        const charCode = StringPrototypeCharCodeAt(char, 0);
-        if (charCode > 0xff) {
-          throw new DOMException(
-            "The string to be encoded contains characters outside of the Latin1 range.",
-            "InvalidCharacterError",
-          );
-        }
-        return charCode;
-      },
-    );
-    return forgivingBase64Encode(TypedArrayFrom(Uint8Array, byteArray));
+    return forgivingBase64Encode(data);
   }
 
   window.__bootstrap.base64 = {
diff --git a/ext/web/internal.d.ts b/ext/web/internal.d.ts
index 41d4c9b325cd22..f0b7ec12d420ef 100644
--- a/ext/web/internal.d.ts
+++ b/ext/web/internal.d.ts
@@ -43,8 +43,8 @@ declare namespace globalThis {
         result: string;
         position: number;
       };
-      forgivingBase64Encode(data: Uint8Array): string;
-      forgivingBase64Decode(data: string): Uint8Array;
+      forgivingBase64Encode(data: string): string;
+      forgivingBase64Decode(data: string): string;
     };
 
     declare var domException: {
diff --git a/ext/web/lib.rs b/ext/web/lib.rs
index b10cb972d1ef2a..64832debc5a267 100644
--- a/ext/web/lib.rs
+++ b/ext/web/lib.rs
@@ -149,8 +149,25 @@ fn op_base64_decode(
   _state: &mut OpState,
   input: String,
   _: (),
-) -> Result<ZeroCopyBuf, AnyError> {
-  let mut input: &str = &input.replace(|c| char::is_ascii_whitespace(&c), "");
+) -> Result<String, AnyError> {
+  let mut ws = false;
+  let len = input.len();
+  let invalid = input.char_indices().any(|(i, c)| {
+    if char::is_ascii_whitespace(&c) {
+      ws = true;
+    } else if c == '=' {
+      if i != len - 1 && i != len - 2 {
+        return true;
+      }
+    } else if c != '+' && c != '/' && !c.is_alphanumeric() {
+      return true;
+    }
+    false
+  });
+
+  // "Remove all ASCII whitespace from data"
+  let input = if ws { input.replace(|c| char::is_ascii_whitespace(&c), "") } else { input };
+  let mut input: &str = &input;
   // "If the length of input divides by 4 leaving no remainder, then:
   //  if input ends with one or two U+003D EQUALS SIGN (=) characters,
   //  remove them from input."
@@ -170,10 +187,8 @@ fn op_base64_decode(
     );
   }
 
-  if input
-    .chars()
-    .any(|c| c != '+' && c != '/' && !c.is_alphanumeric())
-  {
+  // "If data contains a code point that is not '+', '/', or ASCII alphanumeric then return failure."
+  if invalid {
     return Err(
       DomExceptionInvalidCharacterError::new(
         "Failed to decode base64: invalid character",
@@ -190,14 +205,21 @@ fn op_base64_decode(
       err
     ))
   })?;
-  Ok(ZeroCopyBuf::from(out))
+  Ok(String::from_utf8(out).unwrap())
 }
 
 fn op_base64_encode(
   _state: &mut OpState,
-  s: ZeroCopyBuf,
+  s: String,
   _: (),
 ) -> Result<String, AnyError> {
+  let char_count = s.chars().count();
+  let s = s.into_bytes();
+  if s.len() != char_count {
+    // If the byte vec length is longer than the string length, it means that some characters were not respresentable as a single
+    // byte, ie. some characters were not Latin1.
+    return Err(DomExceptionInvalidCharacterError::new("The string to be encoded contains characters outside of the Latin1 range.").into());
+  }
   let cfg = base64::Config::new(base64::CharacterSet::Standard, true)
     .decode_allow_trailing_bits(true);
   let out = base64::encode_config(&s, cfg);