diff --git a/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.cpp b/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.cpp
index e501127acfa..f21b0ca2339 100644
--- a/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.cpp
+++ b/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.cpp
@@ -1397,4 +1397,10 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<JS::ArrayBuffer>> PBKDF2::derive_bits(Algor
     return JS::ArrayBuffer::create(realm, result.release_value());
 }
 
+WebIDL::ExceptionOr<JS::Value> PBKDF2::get_key_length(AlgorithmParams const&)
+{
+    // 1. Return null.
+    return JS::js_null();
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.h b/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.h
index ffcd20aa638..61ad32bacf3 100644
--- a/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.h
+++ b/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.h
@@ -197,6 +197,11 @@ public:
         return WebIDL::NotSupportedError::create(m_realm, "exportKey is not supported"_fly_string);
     }
 
+    virtual WebIDL::ExceptionOr<JS::Value> get_key_length(AlgorithmParams const&)
+    {
+        return WebIDL::NotSupportedError::create(m_realm, "getKeyLength is not supported"_fly_string);
+    }
+
     static NonnullOwnPtr<AlgorithmMethods> create(JS::Realm& realm) { return adopt_own(*new AlgorithmMethods(realm)); }
 
 protected:
@@ -231,6 +236,7 @@ class PBKDF2 : public AlgorithmMethods {
 public:
     virtual WebIDL::ExceptionOr<JS::NonnullGCPtr<CryptoKey>> import_key(AlgorithmParams const&, Bindings::KeyFormat, CryptoKey::InternalKeyData, bool, Vector<Bindings::KeyUsage> const&) override;
     virtual WebIDL::ExceptionOr<JS::NonnullGCPtr<JS::ArrayBuffer>> derive_bits(AlgorithmParams const&, JS::NonnullGCPtr<CryptoKey>, u32) override;
+    virtual WebIDL::ExceptionOr<JS::Value> get_key_length(AlgorithmParams const&) override;
 
     static NonnullOwnPtr<AlgorithmMethods> create(JS::Realm& realm) { return adopt_own(*new PBKDF2(realm)); }
 
diff --git a/Userland/Libraries/LibWeb/Crypto/SubtleCrypto.cpp b/Userland/Libraries/LibWeb/Crypto/SubtleCrypto.cpp
index 074f97e04c2..3fddbdfc777 100644
--- a/Userland/Libraries/LibWeb/Crypto/SubtleCrypto.cpp
+++ b/Userland/Libraries/LibWeb/Crypto/SubtleCrypto.cpp
@@ -677,7 +677,7 @@ SupportedAlgorithmsMap supported_algorithms()
     // https://w3c.github.io/webcrypto/#pbkdf2
     define_an_algorithm<PBKDF2>("importKey"_string, "PBKDF2"_string);
     define_an_algorithm<PBKDF2, PBKDF2Params>("deriveBits"_string, "PBKDF2"_string);
-    // FIXME: define_an_algorithm("get key length"_string, "PBKDF2"_string, ""_string);
+    define_an_algorithm<PBKDF2>("get key length"_string, "PBKDF2"_string);
 
     // https://w3c.github.io/webcrypto/#rsa-oaep
     define_an_algorithm<RSAOAEP, RsaHashedKeyGenParams>("generateKey"_string, "RSA-OAEP"_string);