diff --git a/YOGA_DEFS b/YOGA_DEFS
index 1c71e4c0..bb706632 100644
--- a/YOGA_DEFS
+++ b/YOGA_DEFS
@@ -1,3 +1,7 @@
+with allow_unsafe_import():
+  import os.path
+def isdir(filename):
+  return os.path.isdir(filename)
 
 YOGA_ROOT = '//...'
 JAVA_TARGET = '//java:java'
diff --git a/csharp/BUCK b/csharp/BUCK
index bc6fc3a4..de1e9a39 100644
--- a/csharp/BUCK
+++ b/csharp/BUCK
@@ -35,7 +35,7 @@ cxx_library(
   visibility = ['PUBLIC'],
 )
 
-if py_sdk.os.path.isdir('/Applications/Xcode.app'):
+if isdir('/Applications/Xcode.app'):
   yoganet_ios_srcs = []
   for arch in [
     'iphonesimulator-x86_64', 'iphonesimulator-i386', 'iphoneos-arm64', 'iphoneos-armv7'