diff --git a/lib/github/ldap/filter.rb b/lib/github/ldap/filter.rb
index f11934d..a238642 100644
--- a/lib/github/ldap/filter.rb
+++ b/lib/github/ldap/filter.rb
@@ -20,26 +20,31 @@ module GitHub
 
       # Filter to check group membership.
       #
-      # entry:    finds groups this Net::LDAP::Entry is a member of (optional)
-      # uid_attr: specifies the memberUid attribute to match with   (optional)
+      # entry: finds groups this Net::LDAP::Entry is a member of (optional)
       #
       # Returns a Net::LDAP::Filter.
-      def member_filter(entry = nil, uid_attr = @ldap.uid)
+      def member_filter(entry = nil)
         if entry
-          filter =
-            MEMBERSHIP_NAMES. map {|n| Net::LDAP::Filter.eq(n, entry.dn) }.
-                              reduce(:|)
-
-          if !entry[uid_attr].empty?
-            filter |=
-              entry[uid_attr].map { |uid| Net::LDAP::Filter.eq("memberUid", uid) }.
-                              reduce(:|)
-          end
-
-          filter
+          MEMBERSHIP_NAMES.
+            map {|n| Net::LDAP::Filter.eq(n, entry.dn) }.reduce(:|)
         else
-          (MEMBERSHIP_NAMES + %w(memberUid)).
-            map {|n| Net::LDAP::Filter.pres(n)}.reduce(:|)
+          MEMBERSHIP_NAMES.
+            map {|n| Net::LDAP::Filter.pres(n) }.        reduce(:|)
+        end
+      end
+
+      # Filter to check group membership for posixGroups.
+      #
+      # Used by Domain#membership when posix_support_enabled? is true.
+      #
+      # entry:    finds groups this Net::LDAP::Entry is a member of
+      # uid_attr: specifies the memberUid attribute to match with
+      #
+      # Returns a Net::LDAP::Filter or nil if no entry has no UID set.
+      def posix_member_filter(entry, uid_attr)
+        if !entry[uid_attr].empty?
+          entry[uid_attr].map { |uid| Net::LDAP::Filter.eq("memberUid", uid) }.
+                          reduce(:|)
         end
       end
 
diff --git a/test/filter_test.rb b/test/filter_test.rb
index 0fff2ce..8fc6ba2 100644
--- a/test/filter_test.rb
+++ b/test/filter_test.rb
@@ -24,18 +24,22 @@ class FilterTest < Minitest::Test
   end
 
   def test_member_present
-    assert_equal "(|(|(member=*)(uniqueMember=*))(memberUid=*))", @subject.member_filter.to_s
+    assert_equal "(|(member=*)(uniqueMember=*))", @subject.member_filter.to_s
   end
 
   def test_member_equal
-    assert_equal "(|(|(member=#{@me})(uniqueMember=#{@me}))(memberUid=#{@uid}))",
+    assert_equal "(|(member=#{@me})(uniqueMember=#{@me}))",
                  @subject.member_filter(@entry).to_s
   end
 
-  def test_member_without_uid
+  def test_posix_member_without_uid
     @entry.uid = nil
-    assert_equal "(|(member=#{@me})(uniqueMember=#{@me}))",
-                 @subject.member_filter(@entry).to_s
+    assert_nil @subject.posix_member_filter(@entry, @ldap.uid)
+  end
+
+  def test_posix_member_equal
+    assert_equal "(memberUid=#{@uid})",
+                 @subject.posix_member_filter(@entry, @ldap.uid).to_s
   end
 
   def test_groups_reduced