diff --git a/app/models/wiki_service.rb b/app/models/wiki_service.rb
index c68fd0ff..bec013e7 100644
--- a/app/models/wiki_service.rb
+++ b/app/models/wiki_service.rb
@@ -8,6 +8,7 @@ require 'web'
 require 'page'
 require 'author'
 require 'file_yard'
+require 'instiki_errors'
 
 module AbstractWikiService
 
@@ -77,7 +78,15 @@ module AbstractWikiService
   def edit_web(old_address, new_address, name, markup, color, additional_style, safe_mode = false, 
       password = nil, published = false, brackets_only = false, count_pages = false, 
       allow_uploads = true, max_upload_size = nil)
+
+    if not @webs.key? old_address
+      raise Instiki::ValidationError.new("Web with address '#{old_address}' does not exist")
+    end
+
     if old_address != new_address
+      if @webs.key? new_address
+        raise Instiki::ValidationError.new("There is already a web with address '#{new_address}'")
+      end
       @webs[new_address] = @webs[old_address]
       @webs.delete(old_address)
       @webs[new_address].address = new_address
diff --git a/test/functional/wiki_controller_test.rb b/test/functional/wiki_controller_test.rb
index 84c7532a..810dbe2b 100755
--- a/test/functional/wiki_controller_test.rb
+++ b/test/functional/wiki_controller_test.rb
@@ -131,7 +131,7 @@ class WikiControllerTest < Test::Unit::TestCase
     end
 
   else
-    puts 'Warning: tests involving pdflatex are very slow, therefore they are disable by default.'
+    puts 'Warning: tests involving pdflatex are very slow, therefore they are disabled by default.'
     puts '         Set environment variable INSTIKI_TEST_PDFLATEX or global Ruby variable'
     puts '         $INSTIKI_TEST_PDFLATEX to enable them.'
   end
diff --git a/test/unit/wiki_service_test.rb b/test/unit/wiki_service_test.rb
index d5f16246..c02c61ff 100755
--- a/test/unit/wiki_service_test.rb
+++ b/test/unit/wiki_service_test.rb
@@ -69,6 +69,19 @@ class WikiServiceTest < Test::Unit::TestCase
     assert_equal(@s.storage_path + '/instiki', file_yard.files_path)
   end
 
+  def test_edit_web_validations
+    another_web = @s.create_web 'Another', 'another'
+    
+    # try to rename instiki web to another (which is the name of an already existing one)
+    assert_raises(Instiki::ValidationError) {
+      @s.edit_web('instiki', 'another', @web.name, @web.markup, @web.color, @web.additional_style)
+    }
+
+    assert_raises(Instiki::ValidationError) {
+      @s.edit_web('nonexistant', 'another', @web.name, @web.markup, @web.color, @web.additional_style)
+    }
+  end
+
 
   # Checks that a method call or a block doesn;t change the persisted state of the wiki
   # Usage: