diff --git a/src/auth/scram.ts b/src/auth/scram.ts
index 39b505a..94eaca5 100644
--- a/src/auth/scram.ts
+++ b/src/auth/scram.ts
@@ -6,6 +6,7 @@ import { MongoDriverError } from "../error.ts";
 import { b64, Binary, crypto as stdCrypto, Document, hex } from "../../deps.ts";
 import { driverMetadata } from "../protocol/mod.ts";
 import { pbkdf2 } from "./pbkdf2.ts";
+import { decodeBase64 } from "../utils/decode_base64.ts";
 
 type CryptoMethod = "sha1" | "sha256";
 
@@ -160,7 +161,7 @@ export async function continueScramConversation(
   const withoutProof = `c=biws,r=${rnonce}`;
   const saltedPassword = await HI(
     processedPassword,
-    b64.decode(salt),
+    decodeBase64(salt),
     iterations,
     cryptoMethod,
   );
@@ -193,7 +194,7 @@ export async function continueScramConversation(
   );
   if (
     !compareDigest(
-      b64.decode(parsedResponse.v),
+      decodeBase64(parsedResponse.v),
       new Uint8Array(serverSignature),
     )
   ) {
diff --git a/src/utils/decode_base64.ts b/src/utils/decode_base64.ts
new file mode 100644
index 0000000..ca702fe
--- /dev/null
+++ b/src/utils/decode_base64.ts
@@ -0,0 +1,25 @@
+export function decodeBase64(b64: string): Uint8Array {
+  const chars =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+  let base64 = b64.replace(/-/g, "+").replace(/_/g, "/");
+
+  while (base64.length % 4) {
+    base64 += "=";
+  }
+
+  let bitString = "";
+  for (let i = 0; i < base64.length; i++) {
+    const char = base64.charAt(i);
+    if (char !== "=") {
+      const charIndex = chars.indexOf(char);
+      bitString += charIndex.toString(2).padStart(6, "0");
+    }
+  }
+
+  const bytes = new Uint8Array(bitString.length / 8);
+  for (let i = 0; i < bytes.length; i++) {
+    bytes[i] = parseInt(bitString.substring(8 * i, 8 * (i + 1)), 2);
+  }
+
+  return bytes;
+}
diff --git a/tests/cases/11_decode_base64.ts b/tests/cases/11_decode_base64.ts
new file mode 100644
index 0000000..4d679e0
--- /dev/null
+++ b/tests/cases/11_decode_base64.ts
@@ -0,0 +1,41 @@
+import { decodeBase64 } from "../../src/utils/decode_base64.ts";
+
+import { assertEquals, describe, it } from "./../test.deps.ts";
+
+describe("decodeBase64", () => {
+  it({
+    name: "should correctly decode a standard base64 encoded string",
+    fn() {
+      const encoded = "SGVsbG8gV29ybGQ="; // "Hello World" in base64
+      const decoded = decodeBase64(encoded);
+      assertEquals(new TextDecoder().decode(decoded), "Hello World");
+    },
+  });
+
+  it({
+    name: "should correctly decode a URL-safe base64 encoded string",
+    fn() {
+      const encoded = "SGVsbG8tV29ybGRf"; // URL-safe base64 variant
+      const decoded = decodeBase64(encoded);
+      assertEquals(new TextDecoder().decode(decoded), "Hello-World_");
+    },
+  });
+
+  it({
+    name: "should handle base64 strings with missing padding",
+    fn() {
+      const encoded = "SGVsbG8gV29ybGQ"; // Missing '=' at the end
+      const decoded = decodeBase64(encoded);
+      assertEquals(new TextDecoder().decode(decoded), "Hello World");
+    },
+  });
+
+  it({
+    name: "should return an empty array for an empty string",
+    fn() {
+      const encoded = "";
+      const decoded = decodeBase64(encoded);
+      assertEquals(decoded.length, 0);
+    },
+  });
+});