diff --git a/lib/milia.rb b/lib/milia.rb
index 59239ee..25dd091 100644
--- a/lib/milia.rb
+++ b/lib/milia.rb
@@ -3,6 +3,7 @@
 require File.dirname(__FILE__) + '/milia/control'
 require File.dirname(__FILE__) + '/milia/password_generator'
 require File.dirname(__FILE__) + '/milia/invite_member'
+require File.dirname(__FILE__) + '/milia/support'
 
 require File.dirname(__FILE__) + '/milia/railtie' if defined?(Rails::Railtie)
 
diff --git a/lib/milia/base.rb b/lib/milia/base.rb
index 5755013..7b7a75d 100644
--- a/lib/milia/base.rb
+++ b/lib/milia/base.rb
@@ -77,9 +77,7 @@ def acts_as_universal_and_determines_account()
 
         # validate that a tenant exists prior to a user creation
         before_create do |new_user|
-          if Thread.current[:tenant_id].blank? ||
-              !Thread.current[:tenant_id].kind_of?(Integer) ||
-              Thread.current[:tenant_id].zero?
+          unless Milia::Support::valid_tenant_id?(Thread.current[:tenant_id])
 
             raise ::Milia::Control::InvalidTenantAccess, "no existing valid current tenant"
 
@@ -90,7 +88,7 @@ def acts_as_universal_and_determines_account()
         after_create do |new_user|
           tenant = Tenant.find(Thread.current[:tenant_id])
           unless tenant.users.include?(new_user)
-						new_user.skip_reconfirmation! # For details why this is needed see milia issue #68
+            new_user.skip_reconfirmation! # For details why this is needed see milia issue #68
             tenant.users << new_user # add user to this tenant if not already there
           end
         end # before_create do
@@ -153,6 +151,8 @@ def set_current_tenant(tenant)
             tenant_id = tenant.id
           when Integer then
             tenant_id = tenant
+          when String then
+            tenant_id = tenant
           else
             raise ArgumentError, "invalid tenant object or id"
         end # case
@@ -175,7 +175,9 @@ def set_current_tenant(tenant)
 # for each of the subordinate models in the join seems like a nice safety issue.
 # ------------------------------------------------------------------------
       def where_restrict_tenant(*args)
-        args.map { |klass| "#{klass.table_name}.tenant_id = #{Thread.current[:tenant_id]}" }.join(" AND ")
+        tenant_id = Thread.current[:tenant_id]
+        clause = args.map { |klass| "#{klass.table_name}.tenant_id = ?" }.join(" AND ")
+        clause.gsub('?', (tenant_id.kind_of?(String) ? "'#{tenant_id}'" : tenant_id.to_s))
       end
 
 # ------------------------------------------------------------------------
diff --git a/lib/milia/support.rb b/lib/milia/support.rb
new file mode 100644
index 0000000..9cfef28
--- /dev/null
+++ b/lib/milia/support.rb
@@ -0,0 +1,14 @@
+module Milia
+  module Support
+
+    # Validate the content and type of the given tenant_id. Currently
+    # Integers and Strings (UUID) are supported.
+    def self.valid_tenant_id?(tenant_id)
+      return false if tenant_id.blank?
+      return false if tenant_id.kind_of?(Integer) && tenant_id.zero?
+      return false if !(tenant_id.kind_of?(Integer) || tenant_id.kind_of?(String))
+      true
+    end
+
+  end
+end
diff --git a/test/Gemfile.lock b/test/Gemfile.lock
index a492ba0..fac55f6 100644
--- a/test/Gemfile.lock
+++ b/test/Gemfile.lock
@@ -71,7 +71,7 @@ GIT
       thor (>= 0.18.1, < 2.0)
 
 PATH
-  remote: ../../milia
+  remote: ..
   specs:
     milia (1.3.1)
       devise (~> 4.2)
@@ -240,4 +240,4 @@ RUBY VERSION
    ruby 2.3.1p112
 
 BUNDLED WITH
-   1.13.7
+   1.15.1
diff --git a/test/test/fixtures/tenants.yml b/test/test/fixtures/tenants.yml
index 7a0c5a5..9dd0eeb 100644
--- a/test/test/fixtures/tenants.yml
+++ b/test/test/fixtures/tenants.yml
@@ -10,3 +10,7 @@ tenant_3:
   id: 3
   name: tenant_3
 
+tenant_4:
+  id: 'AAAAAAAA-AAAA-AAAA-AAAA-AAAAAAAAAAAA'
+  name: tenant_4
+
diff --git a/test/test/models/tenant_test.rb b/test/test/models/tenant_test.rb
index 39f1756..bd5872e 100644
--- a/test/test/models/tenant_test.rb
+++ b/test/test/models/tenant_test.rb
@@ -134,19 +134,32 @@ class TenantTest < ActiveSupport::TestCase
       assert_equal  tenants( :tenant_3 ).id, Tenant.current_tenant_id
     end  # should do
 
+    should 'set current tenant - tenant id as string' do
+      assert_equal  tenants( :tenant_1 ).id, Tenant.current_tenant_id
+      Tenant.set_current_tenant( 'AA-AA-AA-AA' )
+      assert_equal  'AA-AA-AA-AA', Tenant.current_tenant_id
+    end  # should do
+
     should 'NOT set current tenant - invalid arg' do
       assert_equal  tenants( :tenant_1 ).id, Tenant.current_tenant_id
       assert_raise(ArgumentError) {
-        Tenant.set_current_tenant( '2' )
+        Tenant.set_current_tenant( 2.2 )
       }
       assert_equal  tenants( :tenant_1 ).id, Tenant.current_tenant_id
     end  # should do
 
 RESTRICT_SNIPPET = 'posts.tenant_id = 1 AND zines.tenant_id = 1'
     should 'prepare a restrict tenant snippet' do
+      Tenant.set_current_tenant( tenants( :tenant_1 ).id )
       assert_equal RESTRICT_SNIPPET, Tenant.where_restrict_tenant( Post, Zine )
     end  # should do
 
+RESTRICT_STRING_SNIPPET = "posts.tenant_id = 'AA-AA-AA-AA' AND zines.tenant_id = 'AA-AA-AA-AA'"
+    should 'prepare a restrict tenant snippet with strings' do
+      Tenant.set_current_tenant( 'AA-AA-AA-AA' )
+      assert_equal RESTRICT_STRING_SNIPPET, Tenant.where_restrict_tenant( Post, Zine )
+    end  # should do
+
     should 'clear tenant.users when tenant destroyed' do
       target = tenants(:tenant_2)
       Tenant.set_current_tenant( target )
diff --git a/test/test/models/user_test.rb b/test/test/models/user_test.rb
index effcdd9..8e47516 100644
--- a/test/test/models/user_test.rb
+++ b/test/test/models/user_test.rb
@@ -102,7 +102,7 @@ class UserTest < ActiveSupport::TestCase
 
     should 'NOT create new user when invalid current tenant - string' do
               # force the current_tenant to be unexpected object
-      Thread.current[:tenant_id] = 'peanut clusters'
+      Thread.current[:tenant_id] = 2.2
 
       assert_no_difference("User.count") do
         assert_raise(::Milia::Control::InvalidTenantAccess,