diff --git a/xpcom/io/nsLocalFileUnix.cpp b/xpcom/io/nsLocalFileUnix.cpp
index 88be319d1820..45112b5a0c95 100644
--- a/xpcom/io/nsLocalFileUnix.cpp
+++ b/xpcom/io/nsLocalFileUnix.cpp
@@ -119,6 +119,7 @@ static nsresult MacErrorMapper(OSErr inErr);
 #ifdef ANDROID
 #include "AndroidBridge.h"
 #include "nsIMIMEService.h"
+#include <linux/magic.h>
 #endif
 
 #include "nsNativeCharsetUtils.h"
@@ -1103,9 +1104,20 @@ nsLocalFile::SetPermissions(PRUint32 aPermissions)
      * Race condition here: we should use fchmod instead, there's no way to 
      * guarantee the name still refers to the same file.
      */
-    if (chmod(mPath.get(), aPermissions) < 0)
-        return NSRESULT_FOR_ERRNO();
-    return NS_OK;
+    if (chmod(mPath.get(), aPermissions) >= 0)
+        return NS_OK;
+#if defined(ANDROID) && defined(STATFS)
+    // For the time being, this is restricted for use by Android, but we 
+    // will figure out what to do for all platforms in bug 638503
+    struct STATFS sfs;
+    if (STATFS(mPath.get(), &sfs) < 0)
+         return NSRESULT_FOR_ERRNO();
+
+    // if this is a FAT file system we can't set file permissions
+    if (sfs.f_type == MSDOS_SUPER_MAGIC )
+        return NS_OK;
+#endif
+    return NSRESULT_FOR_ERRNO();
 }
 
 NS_IMETHODIMP