diff --git a/python/setup.py.in b/python/setup.py.in
index 340691769c..baef4f5554 100644
--- a/python/setup.py.in
+++ b/python/setup.py.in
@@ -181,7 +181,9 @@ else:
     # We cannot find the JSBSim library so the Python module must be built from
     # the sources.
     if compiler.compiler_type == 'msvc':
-        compile_flags = [('/D'+flag).replace('"', '\\"') for flag in ['_USE_MATH_DEFINES', 'NOMINMAX', ${JSBSIM_FLAGS}]]
+        compile_flags = ['/D'+flag for flag in ['_USE_MATH_DEFINES', 'NOMINMAX', ${JSBSIM_FLAGS}]]
+        if sys.version_info < (3,9):
+            compile_flags = [flag.replace('"', '\\"') for flag in compile_flags]
     else:
         compile_flags = ['-D'+flag for flag in [${JSBSIM_FLAGS}]]