diff --git a/Web/Plugins/Core.hs b/Web/Plugins/Core.hs
--- a/Web/Plugins/Core.hs
+++ b/Web/Plugins/Core.hs
@@ -488,7 +488,7 @@
       isDigitChar c    = (c >= '0' && c <= '9')
 
       isOk :: Char -> Bool
-      isOk c = isAlphaChar c || isDigitChar c || c `elem` ":@$-_.~"
+      isOk c = isAlphaChar c || isDigitChar c || elem c (":@$-_.~" :: String)
 
       escapeChar c
           | c == ' '  = singleton '+'
diff --git a/web-plugins.cabal b/web-plugins.cabal
--- a/web-plugins.cabal
+++ b/web-plugins.cabal
@@ -1,5 +1,5 @@
 name:                web-plugins
-version:             0.2.7
+version:             0.2.8
 synopsis:            dynamic plugin system for web applications
 homepage:            http://www.happstack.com/
 license:             BSD3