diff --git a/python.cmake b/python.cmake
index ea47a90ee..12de4e9c6 100644
--- a/python.cmake
+++ b/python.cmake
@@ -292,9 +292,7 @@ macro(FINDPYTHON)
   message(STATUS "PythonLibraryDirs: ${PYTHON_LIBRARY_DIRS}")
   message(STATUS "PythonLibVersionString: ${PYTHONLIBS_VERSION_STRING}")
 
-  if(PYTHON_SITELIB)
-    file(TO_CMAKE_PATH "${PYTHON_SITELIB}" PYTHON_SITELIB)
-  else()
+  if(NOT PYTHON_SITELIB)
     # Use either site-packages (default) or dist-packages (Debian packages)
     # directory
     option(PYTHON_DEB_LAYOUT "Enable Debian-style Python package layout" OFF)
@@ -351,6 +349,11 @@ macro(FINDPYTHON)
     endif()
   endif()
 
+  # Avoid paths in Windows format
+  if(PYTHON_SITELIB)
+    file(TO_CMAKE_PATH "${PYTHON_SITELIB}" PYTHON_SITELIB)
+  endif()
+
   message(STATUS "Python site lib: ${PYTHON_SITELIB}")
   message(STATUS "Python include dirs: ${PYTHON_INCLUDE_DIRS}")