diff --git a/emsdk b/emsdk
index 644836d..a5e23eb 100644
--- a/emsdk
+++ b/emsdk
@@ -406,10 +406,15 @@ class Tool:
   
   def compatible_with_this_os(self):
     if hasattr(self, 'os'):
+      if self.os == 'all':
+        return True
       if (WINDOWS and 'win' in self.os) or (LINUX and 'linux' in self.os) or (OSX and 'osx' in self.os):
         return True
       else:
         return False
+    else:
+      if not hasattr(self, 'osx_url') and not hasattr(self, 'windows_url') and not hasattr(self, 'unix_url'):
+        return True
 
     if OSX and hasattr(self, 'osx_url'):
       return True
@@ -506,7 +511,7 @@ class Tool:
         if not success:
           return False
         print "Done."
-        return True
+      return True
     else:
       url = self.download_url()
       if hasattr(self, 'git_branch'):