diff --git a/Tests/LibWasm/test-wasm.cpp b/Tests/LibWasm/test-wasm.cpp
index f761a742435..e748ae5f71a 100644
--- a/Tests/LibWasm/test-wasm.cpp
+++ b/Tests/LibWasm/test-wasm.cpp
@@ -8,6 +8,7 @@
 #include <LibTest/JavaScriptTestRunner.h>
 #include <LibWasm/AbstractMachine/BytecodeInterpreter.h>
 #include <LibWasm/Types.h>
+#include <string.h>
 
 TEST_ROOT("Userland/Libraries/LibWasm/Tests");
 
@@ -16,7 +17,7 @@ TESTJS_GLOBAL_FUNCTION(read_binary_wasm_file, readBinaryWasmFile)
     auto filename = TRY(vm.argument(0).to_string(global_object));
     auto file = Core::File::open(filename, Core::OpenMode::ReadOnly);
     if (file.is_error())
-        return vm.throw_completion<JS::TypeError>(global_object, file.error().string());
+        return vm.throw_completion<JS::TypeError>(global_object, strerror(file.error().code()));
     auto contents = file.value()->read_all();
     auto array = JS::Uint8Array::create(global_object, contents.size());
     contents.span().copy_to(array->data());
diff --git a/Userland/Applications/FontEditor/GlyphEditorWidget.cpp b/Userland/Applications/FontEditor/GlyphEditorWidget.cpp
index a36b3586bbf..d4877bca4ed 100644
--- a/Userland/Applications/FontEditor/GlyphEditorWidget.cpp
+++ b/Userland/Applications/FontEditor/GlyphEditorWidget.cpp
@@ -11,6 +11,7 @@
 #include <LibGUI/Painter.h>
 #include <LibGfx/BitmapFont.h>
 #include <LibGfx/Palette.h>
+#include <string.h>
 
 static int x_offset;
 static int y_offset;
diff --git a/Userland/Applications/HexEditor/HexEditor.cpp b/Userland/Applications/HexEditor/HexEditor.cpp
index e4ec9af54ea..35dc37f6ec6 100644
--- a/Userland/Applications/HexEditor/HexEditor.cpp
+++ b/Userland/Applications/HexEditor/HexEditor.cpp
@@ -23,6 +23,7 @@
 #include <ctype.h>
 #include <fcntl.h>
 #include <stdio.h>
+#include <string.h>
 #include <unistd.h>
 
 HexEditor::HexEditor()
diff --git a/Userland/Applications/PixelPaint/Image.cpp b/Userland/Applications/PixelPaint/Image.cpp
index dca4e320e50..25b60c704b4 100644
--- a/Userland/Applications/PixelPaint/Image.cpp
+++ b/Userland/Applications/PixelPaint/Image.cpp
@@ -159,7 +159,7 @@ Result<void, String> Image::write_to_file(const String& file_path) const
 
     auto file_or_error = Core::File::open(file_path, (Core::OpenMode)(Core::OpenMode::WriteOnly | Core::OpenMode::Truncate));
     if (file_or_error.is_error())
-        return String { file_or_error.error().string() };
+        return String { strerror(file_or_error.error().code()) };
 
     if (!file_or_error.value()->write(builder.string_view()))
         return String { file_or_error.value()->error_string() };
diff --git a/Userland/Applications/PixelPaint/PaletteWidget.cpp b/Userland/Applications/PixelPaint/PaletteWidget.cpp
index bae64b426c0..d5adcf290cd 100644
--- a/Userland/Applications/PixelPaint/PaletteWidget.cpp
+++ b/Userland/Applications/PixelPaint/PaletteWidget.cpp
@@ -15,6 +15,7 @@
 #include <LibGUI/ColorPicker.h>
 #include <LibGUI/MessageBox.h>
 #include <LibGfx/Palette.h>
+#include <string.h>
 
 REGISTER_WIDGET(PixelPaint, PaletteWidget);
 
@@ -263,7 +264,7 @@ Result<Vector<Color>, String> PaletteWidget::load_palette_path(String const& fil
 {
     auto file_or_error = Core::File::open(file_path, Core::OpenMode::ReadOnly);
     if (file_or_error.is_error())
-        return String { file_or_error.error().string() };
+        return String { strerror(file_or_error.error().code()) };
 
     auto& file = *file_or_error.value();
     return load_palette_file(file);
diff --git a/Userland/Applications/Run/RunWindow.cpp b/Userland/Applications/Run/RunWindow.cpp
index 6964ac3be80..96eb30ce358 100644
--- a/Userland/Applications/Run/RunWindow.cpp
+++ b/Userland/Applications/Run/RunWindow.cpp
@@ -20,6 +20,7 @@
 #include <LibGUI/Widget.h>
 #include <spawn.h>
 #include <stdio.h>
+#include <string.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
diff --git a/Userland/Applications/Spreadsheet/ExportDialog.cpp b/Userland/Applications/Spreadsheet/ExportDialog.cpp
index 62a82f53be2..680d770e66f 100644
--- a/Userland/Applications/Spreadsheet/ExportDialog.cpp
+++ b/Userland/Applications/Spreadsheet/ExportDialog.cpp
@@ -22,6 +22,7 @@
 #include <LibGUI/TextBox.h>
 #include <LibGUI/Wizards/WizardDialog.h>
 #include <LibGUI/Wizards/WizardPage.h>
+#include <string.h>
 #include <unistd.h>
 
 // This is defined in ImportDialog.cpp, we can't include it twice, since the generated symbol is exported.
diff --git a/Userland/Applications/Spreadsheet/Readers/Test/TestXSV.cpp b/Userland/Applications/Spreadsheet/Readers/Test/TestXSV.cpp
index 5dbe2a59661..0103e4c6c04 100644
--- a/Userland/Applications/Spreadsheet/Readers/Test/TestXSV.cpp
+++ b/Userland/Applications/Spreadsheet/Readers/Test/TestXSV.cpp
@@ -10,6 +10,7 @@
 #include "../XSV.h"
 #include <AK/ByteBuffer.h>
 #include <LibCore/File.h>
+#include <string.h>
 
 TEST_CASE(should_parse_valid_data)
 {
diff --git a/Userland/Applications/Spreadsheet/Workbook.cpp b/Userland/Applications/Spreadsheet/Workbook.cpp
index 40c94e12fe6..df9b331d4ea 100644
--- a/Userland/Applications/Spreadsheet/Workbook.cpp
+++ b/Userland/Applications/Spreadsheet/Workbook.cpp
@@ -51,7 +51,7 @@ Result<bool, String> Workbook::load(const StringView& filename)
         sb.append("Failed to open ");
         sb.append(filename);
         sb.append(" for reading. Error: ");
-        sb.append(file_or_error.error().string());
+        sb.appendff("{}", file_or_error.error());
 
         return sb.to_string();
     }
diff --git a/Userland/Libraries/LibCore/File.cpp b/Userland/Libraries/LibCore/File.cpp
index 141163b3548..184042d5693 100644
--- a/Userland/Libraries/LibCore/File.cpp
+++ b/Userland/Libraries/LibCore/File.cpp
@@ -27,11 +27,11 @@
 
 namespace Core {
 
-Result<NonnullRefPtr<File>, OSError> File::open(String filename, OpenMode mode, mode_t permissions)
+ErrorOr<NonnullRefPtr<File>> File::open(String filename, OpenMode mode, mode_t permissions)
 {
     auto file = File::construct(move(filename));
     if (!file->open_impl(mode, permissions))
-        return OSError(file->error());
+        return Error::from_errno(file->error());
     return file;
 }
 
diff --git a/Userland/Libraries/LibCore/File.h b/Userland/Libraries/LibCore/File.h
index 2ec2e8c0a49..34b024b1609 100644
--- a/Userland/Libraries/LibCore/File.h
+++ b/Userland/Libraries/LibCore/File.h
@@ -7,8 +7,6 @@
 #pragma once
 
 #include <AK/Error.h>
-#include <AK/OSError.h>
-#include <AK/Result.h>
 #include <AK/String.h>
 #include <LibCore/IODevice.h>
 #include <sys/stat.h>
@@ -20,7 +18,7 @@ class File final : public IODevice {
 public:
     virtual ~File() override;
 
-    static Result<NonnullRefPtr<File>, OSError> open(String filename, OpenMode, mode_t = 0644);
+    static ErrorOr<NonnullRefPtr<File>> open(String filename, OpenMode, mode_t = 0644);
 
     String filename() const { return m_filename; }
     void set_filename(const String filename) { m_filename = move(filename); }
diff --git a/Userland/Libraries/LibCore/FileStream.h b/Userland/Libraries/LibCore/FileStream.h
index 4069383b371..f8462397d71 100644
--- a/Userland/Libraries/LibCore/FileStream.h
+++ b/Userland/Libraries/LibCore/FileStream.h
@@ -9,6 +9,7 @@
 #include <AK/Buffered.h>
 #include <AK/ByteBuffer.h>
 #include <AK/Stream.h>
+#include <AK/Try.h>
 #include <LibCore/File.h>
 
 namespace Core {
@@ -20,28 +21,18 @@ public:
     {
     }
 
-    static Result<InputFileStream, OSError> open(StringView filename, OpenMode mode = OpenMode::ReadOnly, mode_t permissions = 0644)
+    static ErrorOr<InputFileStream> open(StringView filename, OpenMode mode = OpenMode::ReadOnly, mode_t permissions = 0644)
     {
         VERIFY(has_flag(mode, OpenMode::ReadOnly));
-
-        auto file_result = File::open(filename, mode, permissions);
-
-        if (file_result.is_error())
-            return file_result.error();
-
-        return InputFileStream { file_result.value() };
+        auto file = TRY(File::open(filename, mode, permissions));
+        return InputFileStream { move(file) };
     }
 
-    static Result<Buffered<InputFileStream>, OSError> open_buffered(StringView filename, OpenMode mode = OpenMode::ReadOnly, mode_t permissions = 0644)
+    static ErrorOr<Buffered<InputFileStream>> open_buffered(StringView filename, OpenMode mode = OpenMode::ReadOnly, mode_t permissions = 0644)
     {
         VERIFY(has_flag(mode, OpenMode::ReadOnly));
-
-        auto file_result = File::open(filename, mode, permissions);
-
-        if (file_result.is_error())
-            return file_result.error();
-
-        return Buffered<InputFileStream> { file_result.value() };
+        auto file = TRY(File::open(filename, mode, permissions));
+        return Buffered<InputFileStream> { move(file) };
     }
 
     size_t read(Bytes bytes) override
@@ -89,28 +80,18 @@ public:
     {
     }
 
-    static Result<OutputFileStream, OSError> open(StringView filename, OpenMode mode = OpenMode::WriteOnly, mode_t permissions = 0644)
+    static ErrorOr<OutputFileStream> open(StringView filename, OpenMode mode = OpenMode::WriteOnly, mode_t permissions = 0644)
     {
         VERIFY(has_flag(mode, OpenMode::WriteOnly));
-
-        auto file_result = File::open(filename, mode, permissions);
-
-        if (file_result.is_error())
-            return file_result.error();
-
-        return OutputFileStream { file_result.value() };
+        auto file = TRY(File::open(filename, mode, permissions));
+        return OutputFileStream { move(file) };
     }
 
-    static Result<Buffered<OutputFileStream>, OSError> open_buffered(StringView filename, OpenMode mode = OpenMode::WriteOnly, mode_t permissions = 0644)
+    static ErrorOr<Buffered<OutputFileStream>> open_buffered(StringView filename, OpenMode mode = OpenMode::WriteOnly, mode_t permissions = 0644)
     {
         VERIFY(has_flag(mode, OpenMode::WriteOnly));
-
-        auto file_result = File::open(filename, mode, permissions);
-
-        if (file_result.is_error())
-            return file_result.error();
-
-        return Buffered<OutputFileStream> { file_result.value() };
+        auto file = TRY(File::open(filename, mode, permissions));
+        return Buffered<OutputFileStream> { move(file) };
     }
 
     static OutputFileStream standard_output()
diff --git a/Userland/Libraries/LibGUI/FileIconProvider.cpp b/Userland/Libraries/LibGUI/FileIconProvider.cpp
index a51dbe6be35..82180adee0c 100644
--- a/Userland/Libraries/LibGUI/FileIconProvider.cpp
+++ b/Userland/Libraries/LibGUI/FileIconProvider.cpp
@@ -16,6 +16,7 @@
 #include <LibGUI/Painter.h>
 #include <LibGfx/Bitmap.h>
 #include <LibGfx/PNGLoader.h>
+#include <string.h>
 #include <sys/stat.h>
 #include <unistd.h>
 
diff --git a/Userland/Libraries/LibGfx/BitmapFont.cpp b/Userland/Libraries/LibGfx/BitmapFont.cpp
index 60ad4b16f0a..b97968b0132 100644
--- a/Userland/Libraries/LibGfx/BitmapFont.cpp
+++ b/Userland/Libraries/LibGfx/BitmapFont.cpp
@@ -11,6 +11,7 @@
 #include <LibCore/FileStream.h>
 #include <LibGfx/FontDatabase.h>
 #include <LibGfx/FontStyleMapping.h>
+#include <string.h>
 
 namespace Gfx {
 
diff --git a/Userland/Libraries/LibSQL/Heap.h b/Userland/Libraries/LibSQL/Heap.h
index caef7e8702a..b78b486dda3 100644
--- a/Userland/Libraries/LibSQL/Heap.h
+++ b/Userland/Libraries/LibSQL/Heap.h
@@ -8,6 +8,7 @@
 
 #include <AK/Debug.h>
 #include <AK/HashMap.h>
+#include <AK/Result.h>
 #include <AK/String.h>
 #include <AK/Vector.h>
 #include <LibCore/File.h>
diff --git a/Userland/Libraries/LibWeb/Loader/ResourceLoader.cpp b/Userland/Libraries/LibWeb/Loader/ResourceLoader.cpp
index 1c2bb062088..e87e674d98c 100644
--- a/Userland/Libraries/LibWeb/Loader/ResourceLoader.cpp
+++ b/Userland/Libraries/LibWeb/Loader/ResourceLoader.cpp
@@ -177,9 +177,9 @@ void ResourceLoader::load(LoadRequest& request, Function<void(ReadonlyBytes, con
         auto file_result = Core::File::open(url.path(), Core::OpenMode::ReadOnly);
         if (file_result.is_error()) {
             auto& error = file_result.error();
-            log_failure(request, error.string());
+            log_failure(request, error);
             if (error_callback)
-                error_callback(error.string(), error.error());
+                error_callback(String::formatted("{}", error), error.code());
             return;
         }
 
diff --git a/Userland/Services/FileOperation/main.cpp b/Userland/Services/FileOperation/main.cpp
index 188d472b1f1..5515a3569db 100644
--- a/Userland/Services/FileOperation/main.cpp
+++ b/Userland/Services/FileOperation/main.cpp
@@ -34,7 +34,7 @@ static int perform_delete(Vector<String> const& sources);
 static int execute_work_items(Vector<WorkItem> const& items);
 static void report_error(String message);
 static void report_warning(String message);
-static AK::Result<AK::NonnullRefPtr<Core::File>, AK::OSError> open_destination_file(String const& destination);
+static ErrorOr<NonnullRefPtr<Core::File>> open_destination_file(String const& destination);
 static String deduplicate_destination_file_name(String const& destination);
 
 int main(int argc, char** argv)
@@ -379,10 +379,10 @@ int execute_work_items(Vector<WorkItem> const& items)
     return 0;
 }
 
-AK::Result<AK::NonnullRefPtr<Core::File>, AK::OSError> open_destination_file(String const& destination)
+ErrorOr<NonnullRefPtr<Core::File>> open_destination_file(String const& destination)
 {
     auto destination_file_or_error = Core::File::open(destination, (Core::OpenMode)(Core::OpenMode::WriteOnly | Core::OpenMode::Truncate | Core::OpenMode::MustBeNew));
-    if (destination_file_or_error.is_error() && destination_file_or_error.error().error() == EEXIST) {
+    if (destination_file_or_error.is_error() && destination_file_or_error.error().code() == EEXIST) {
         return open_destination_file(deduplicate_destination_file_name(destination));
     }
     return destination_file_or_error;
diff --git a/Userland/Services/WindowServer/ScreenLayout.ipp b/Userland/Services/WindowServer/ScreenLayout.ipp
index 04c9f4f87ef..877c10db768 100644
--- a/Userland/Services/WindowServer/ScreenLayout.ipp
+++ b/Userland/Services/WindowServer/ScreenLayout.ipp
@@ -9,6 +9,7 @@
 #include <Services/WindowServer/ScreenLayout.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <string.h>
 
 // Must be included after LibIPC/Forward.h
 #include <LibIPC/Decoder.h>
diff --git a/Userland/Utilities/arp.cpp b/Userland/Utilities/arp.cpp
index 11837795ed8..d19a89140de 100644
--- a/Userland/Utilities/arp.cpp
+++ b/Userland/Utilities/arp.cpp
@@ -16,6 +16,7 @@
 #include <net/if_arp.h>
 #include <net/route.h>
 #include <netinet/in.h>
+#include <string.h>
 #include <sys/ioctl.h>
 #include <sys/socket.h>
 #include <unistd.h>
diff --git a/Userland/Utilities/cksum.cpp b/Userland/Utilities/cksum.cpp
index 46250a664c1..be7a6d37115 100644
--- a/Userland/Utilities/cksum.cpp
+++ b/Userland/Utilities/cksum.cpp
@@ -8,6 +8,7 @@
 #include <LibCore/File.h>
 #include <LibCrypto/Checksum/Adler32.h>
 #include <LibCrypto/Checksum/CRC32.h>
+#include <string.h>
 
 int main(int argc, char** argv)
 {
diff --git a/Userland/Utilities/errno.cpp b/Userland/Utilities/errno.cpp
index a95885914af..7618d4c3e50 100644
--- a/Userland/Utilities/errno.cpp
+++ b/Userland/Utilities/errno.cpp
@@ -5,7 +5,7 @@
  */
 
 #include <LibCore/ArgsParser.h>
-#include <LibCore/File.h>
+#include <string.h>
 
 int main(int argc, char** argv)
 {
diff --git a/Userland/Utilities/hexdump.cpp b/Userland/Utilities/hexdump.cpp
index f14eb43a1b2..2a8c08aff32 100644
--- a/Userland/Utilities/hexdump.cpp
+++ b/Userland/Utilities/hexdump.cpp
@@ -8,6 +8,7 @@
 #include <LibCore/ArgsParser.h>
 #include <LibCore/File.h>
 #include <ctype.h>
+#include <string.h>
 
 static constexpr size_t LINE_LENGTH_BYTES = 16;
 
diff --git a/Userland/Utilities/mv.cpp b/Userland/Utilities/mv.cpp
index 29f607d2be5..56cc52343e2 100644
--- a/Userland/Utilities/mv.cpp
+++ b/Userland/Utilities/mv.cpp
@@ -9,6 +9,7 @@
 #include <LibCore/ArgsParser.h>
 #include <LibCore/File.h>
 #include <stdio.h>
+#include <string.h>
 #include <sys/stat.h>
 #include <unistd.h>
 
diff --git a/Userland/Utilities/sql.cpp b/Userland/Utilities/sql.cpp
index d0ae3ab87de..b078b728bde 100644
--- a/Userland/Utilities/sql.cpp
+++ b/Userland/Utilities/sql.cpp
@@ -178,7 +178,7 @@ private:
             auto file_name = m_input_file_chain.take_first();
             auto file_or_error = Core::File::open(file_name, Core::OpenMode::ReadOnly);
             if (file_or_error.is_error()) {
-                warnln("Input file {} could not be opened: {}", file_name, file_or_error.error().string());
+                warnln("Input file {} could not be opened: {}", file_name, file_or_error.error());
                 return {};
             }
             m_input_file = file_or_error.value();