diff --git a/setup.py b/setup.py
index 750f47c..e652969 100644
--- a/setup.py
+++ b/setup.py
@@ -1267,7 +1267,12 @@
                                          '_ctypes', 'libffi'))
             ffi_configfile = os.path.join(ffi_builddir, 'fficonfig.py')
 
-            if self.force or not os.path.exists(ffi_configfile):
+            from distutils.dep_util import newer_group
+
+            config_sources = [os.path.join(ffi_srcdir, fname)
+                              for fname in os.listdir(ffi_srcdir)]
+            if self.force or newer_group(config_sources,
+                                         ffi_configfile):
                 from distutils.dir_util import mkpath
                 mkpath(ffi_builddir)
                 config_args = []