diff --git a/setup.py b/setup.py
index 10992779e..2b457cf05 100755
--- a/setup.py
+++ b/setup.py
@@ -729,7 +729,7 @@ class pil_build_ext(build_ext):
             defs.append(("HAVE_LIBTIFF", None))
             # FIXME the following define should be detected automatically
             #       based on system libtiff, see #4237
-            if PLATFORM_MINGW:
+            if sys.platform == "win32":
                 defs.append(("USE_WIN32_FILEIO", None))
         if feature.xcb:
             libs.append(feature.xcb)
diff --git a/winbuild/tiff.opt b/winbuild/tiff.opt
index d82c51678..d6e7a8ed4 100644
--- a/winbuild/tiff.opt
+++ b/winbuild/tiff.opt
@@ -124,7 +124,7 @@ OPTFLAGS =	/Ox /MD /EHsc /W3 /D_CRT_SECURE_NO_DEPRECATE
 # instead of Windows specific system calls. See notes on top of tif_unix.c
 # module for details.
 #
-USE_WIN_CRT_LIB = 1
+#USE_WIN_CRT_LIB = 1
 
 # Compiler specific options. You may probably want to adjust compilation
 # parameters in CFLAGS variable. Refer to your compiler documentation