diff --git a/.github/actions/build-python-from-source/action.yml b/.github/actions/build-python-from-source/action.yml
index 692130d..2c6580c 100644
--- a/.github/actions/build-python-from-source/action.yml
+++ b/.github/actions/build-python-from-source/action.yml
@@ -65,11 +65,13 @@ runs:
         fi
         # Build it!
         if [ "${{ runner.os }}" != "Windows" ]; then
-          ./configure --prefix=$prefix $configure_options --enable-optimizations
+          ./configure --prefix=$prefix CFLAGS="-O3" CXXFLAGS="-O3" $configure_options
           make -j $(nproc)  # Use all available processors to speed up the build.
         else
           # Use the build script provided for Windows in the Python source.
-          ./PCbuild/build.bat -e -d
+          set CFLAGS=/Ox
+          set CXXFLAGS=/Ox
+          ./PCbuild/build.bat -e -d $configure_options
         fi
 
     # Install the built Python version.
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 2ee1a5f..8423efb 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -27,9 +27,9 @@ jobs:
           #- os: ubuntu-latest
           #  python-version: '3.12.7'
           #  build-from-source: false
-          #- os: ubuntu-latest
-          #  python-version: '3.13.0-rc.3'
-          #  build-from-source: false
+          - os: ubuntu-latest
+            python-version: '3.13.0-rc.3'
+            build-from-source: false
           #- os: windows-latest
           #  python-version: '3.13.0-rc.3'
           #  build-from-source: false
diff --git a/setup.py b/setup.py
index d612176..af243f9 100644
--- a/setup.py
+++ b/setup.py
@@ -26,24 +26,12 @@ def check_venv() -> None:
         )
 
 
-def patch_out() -> None:
-    """
-    Patch out certain modules to prevent import conflicts on Windows.
-    """
-    # On windows mock gets imported from _msvccompiler which then tries to import asyncio
-    # which causes a name conflict on concurrent. This prevents that.
-    if sys.platform.startswith("win"):
-        sys.modules["unittest"] = type(sys)("unittest")
-        sys.modules["unittest.mock"] = type(sys)("mock")
-
-
 def check_compiler() -> None:
     """
     Check the default compiler for the current platform and fix up name clashed on windows.
 
     Prints the found compiler class.
     """
-    patch_out()
     import distutils.ccompiler as cc
 
     plat = os.name