diff --git a/Libraries/LibWeb/DOMURL/DOMURL.cpp b/Libraries/LibWeb/DOMURL/DOMURL.cpp
index fd79e5f4be8..b815f321085 100644
--- a/Libraries/LibWeb/DOMURL/DOMURL.cpp
+++ b/Libraries/LibWeb/DOMURL/DOMURL.cpp
@@ -120,7 +120,7 @@ void DOMURL::visit_edges(Cell::Visitor& visitor)
 }
 
 // https://w3c.github.io/FileAPI/#dfn-createObjectURL
-WebIDL::ExceptionOr<String> DOMURL::create_object_url(JS::VM& vm, GC::Ref<FileAPI::Blob> object)
+WebIDL::ExceptionOr<Utf16String> DOMURL::create_object_url(JS::VM& vm, GC::Ref<FileAPI::Blob> object)
 {
     // The createObjectURL(obj) static method must return the result of adding an entry to the blob URL store for obj.
     return TRY_OR_THROW_OOM(vm, FileAPI::add_entry_to_blob_url_store(object));
diff --git a/Libraries/LibWeb/DOMURL/DOMURL.h b/Libraries/LibWeb/DOMURL/DOMURL.h
index 5869263caac..b21128f8e6f 100644
--- a/Libraries/LibWeb/DOMURL/DOMURL.h
+++ b/Libraries/LibWeb/DOMURL/DOMURL.h
@@ -26,7 +26,7 @@ public:
 
     virtual ~DOMURL() override;
 
-    static WebIDL::ExceptionOr<String> create_object_url(JS::VM&, GC::Ref<FileAPI::Blob> object);
+    static WebIDL::ExceptionOr<Utf16String> create_object_url(JS::VM&, GC::Ref<FileAPI::Blob> object);
     static void revoke_object_url(JS::VM&, StringView url);
 
     static GC::Ptr<DOMURL> parse_for_bindings(JS::VM&, String const& url, Optional<String> const& base = {});
diff --git a/Libraries/LibWeb/DOMURL/DOMURL.idl b/Libraries/LibWeb/DOMURL/DOMURL.idl
index cc468050b43..b7ed30dcfc5 100644
--- a/Libraries/LibWeb/DOMURL/DOMURL.idl
+++ b/Libraries/LibWeb/DOMURL/DOMURL.idl
@@ -24,6 +24,6 @@ interface URL {
 
     USVString toJSON();
 
-    static DOMString createObjectURL(Blob obj); // FIXME: Should be (Blob or MediaSource).
+    static Utf16DOMString createObjectURL(Blob obj); // FIXME: Should be (Blob or MediaSource).
     static undefined revokeObjectURL(DOMString url);
 };
diff --git a/Libraries/LibWeb/FileAPI/BlobURLStore.cpp b/Libraries/LibWeb/FileAPI/BlobURLStore.cpp
index 382a6b2519a..1362abb9641 100644
--- a/Libraries/LibWeb/FileAPI/BlobURLStore.cpp
+++ b/Libraries/LibWeb/FileAPI/BlobURLStore.cpp
@@ -25,10 +25,10 @@ BlobURLStore& blob_url_store()
 }
 
 // https://w3c.github.io/FileAPI/#unicodeBlobURL
-ErrorOr<String> generate_new_blob_url()
+ErrorOr<Utf16String> generate_new_blob_url()
 {
     // 1. Let result be the empty string.
-    StringBuilder result;
+    StringBuilder result { StringBuilder::Mode::UTF16 };
 
     // 2. Append the string "blob:" to result.
     TRY(result.try_append("blob:"sv));
@@ -57,11 +57,11 @@ ErrorOr<String> generate_new_blob_url()
     TRY(result.try_append(uuid));
 
     // 10. Return result.
-    return result.to_string();
+    return result.to_utf16_string();
 }
 
 // https://w3c.github.io/FileAPI/#add-an-entry
-ErrorOr<String> add_entry_to_blob_url_store(GC::Ref<Blob> object)
+ErrorOr<Utf16String> add_entry_to_blob_url_store(GC::Ref<Blob> object)
 {
     // 1. Let store be the user agent’s blob URL store.
     auto& store = blob_url_store();
@@ -73,7 +73,7 @@ ErrorOr<String> add_entry_to_blob_url_store(GC::Ref<Blob> object)
     BlobURLEntry entry { object, HTML::current_principal_settings_object() };
 
     // 4. Set store[url] to entry.
-    TRY(store.try_set(url, move(entry)));
+    TRY(store.try_set(url.to_utf8_but_should_be_ported_to_utf16(), move(entry)));
 
     // 5. Return url.
     return url;
diff --git a/Libraries/LibWeb/FileAPI/BlobURLStore.h b/Libraries/LibWeb/FileAPI/BlobURLStore.h
index 1b4c8176391..b709f214481 100644
--- a/Libraries/LibWeb/FileAPI/BlobURLStore.h
+++ b/Libraries/LibWeb/FileAPI/BlobURLStore.h
@@ -25,8 +25,8 @@ struct BlobURLEntry {
 using BlobURLStore = HashMap<String, BlobURLEntry>;
 
 BlobURLStore& blob_url_store();
-ErrorOr<String> generate_new_blob_url();
-ErrorOr<String> add_entry_to_blob_url_store(GC::Ref<Blob> object);
+ErrorOr<Utf16String> generate_new_blob_url();
+ErrorOr<Utf16String> add_entry_to_blob_url_store(GC::Ref<Blob> object);
 bool check_for_same_partition_blob_url_usage(URL::BlobURLEntry const&, GC::Ref<HTML::Environment>);
 struct NavigationEnvironment { };
 Optional<URL::BlobURLEntry::Object> obtain_a_blob_object(URL::BlobURLEntry const&, Variant<GC::Ref<HTML::Environment>, NavigationEnvironment> environment);