diff --git a/History.rdoc b/History.rdoc
index b90652c..80da1ba 100644
--- a/History.rdoc
+++ b/History.rdoc
@@ -2,6 +2,7 @@
 
 === Changes
   * Rename `url_whitelist` to `url_allowlist`
+  * Allowlist now supports regular expressions
 
 === Breaking changes
   * Failed checks against the allowlist now raise `UrlNotAllowed` rather than `NotWhitelistedUrl`
diff --git a/README.markdown b/README.markdown
index 290566e..3e18fc3 100644
--- a/README.markdown
+++ b/README.markdown
@@ -349,10 +349,13 @@ to one of the values specified in the url allowlist like so:
 DatabaseCleaner.url_allowlist = ['postgres://postgres@localhost', 'postgres://foo@bar']
 ```
 
-Allowlist elements may be specified as regular expressions if extra flexibility is required::
+Allowlist elements are matched with case equality (`===`), so regular expressions or procs may be used:
 
 ```ruby
-DatabaseCleaner.url_allowlist = [%r{^postgres://postgres@localhost}]
+DatabaseCleaner.url_allowlist = [
+  %r{^postgres://postgres@localhost},         # match any db with this prefix
+  proc {|uri| URI.parse(uri).user == "test" } # match any db authenticating with the 'test' user
+]
 ```
 
 ## COPYRIGHT
diff --git a/spec/database_cleaner/safeguard_spec.rb b/spec/database_cleaner/safeguard_spec.rb
index 20b7993..89d8656 100644
--- a/spec/database_cleaner/safeguard_spec.rb
+++ b/spec/database_cleaner/safeguard_spec.rb
@@ -122,9 +122,24 @@ module DatabaseCleaner
               expect { cleaner.start }.to raise_error(Safeguard::Error::UrlNotAllowed)
             end
           end
+
+          describe 'A url that matches a proc' do
+            let(:database_url) { 'redis://test:test@foo.bar' }
+
+            it 'does not raise' do
+              expect { cleaner.start }.to_not raise_error
+            end
+          end
         end
 
-        let(:url_allowlist) { ['postgres://postgres@localhost', 'postgres://foo.bar', %r{^postgres://bar.baz}] }
+        let(:url_allowlist) do
+          [
+            'postgres://postgres@localhost',
+            'postgres://foo.bar',
+            %r{^postgres://bar.baz},
+            proc { |x| URI.parse(x).user == 'test' }
+          ]
+        end
 
         describe 'url_allowlist' do
           before { DatabaseCleaner.url_allowlist = url_allowlist }