Index: twisted/web2/static.py
===================================================================
--- twisted/web2/static.py      (revision 15884)
+++ twisted/web2/static.py      (working copy)
@@ -17,7 +17,7 @@
 
 # Twisted Imports
 from twisted.python import filepath
-from twisted.internet.defer import succeed, maybeDeferred
+from twisted.internet.defer import maybeDeferred
 from zope.interface import implements
 
 class MetaDataMixin(object):
@@ -74,6 +74,17 @@
         return True
 
 class StaticRenderMixin(resource.RenderMixin, MetaDataMixin):
+    def checkPreconditions(self, request):
+        if request.method not in ("GET", "HEAD"):
+            http.checkPreconditions(
+                request,
+                entityExists = self.exists(),
+                etag         = self.etag(),
+                lastModified = self.lastModified(),
+            )
+
+        super(StaticRenderMixin, self).checkPreconditions(request)
+
     def renderHTTP(self, request):
         """
         See L{resource.RenderMixIn.renderHTTP}.
Index: twisted/web2/resource.py
===================================================================
--- twisted/web2/resource.py    (revision 15882)
+++ twisted/web2/resource.py    (working copy)
@@ -25,6 +25,28 @@
             self._allowed_methods = tuple([name[5:] for name in dir(self) if name.startswith('http_')])
         return self._allowed_methods
 
+    def checkPreconditions(self, request):
+        """
+        Checks all preconditions imposed by this resource upon a request made
+        against it.
+        @param request: the request to process.
+        @raise http.HTTPError: if any precondition fails.
+        """
+        #
+        # http.checkPreconditions() gets called by the server after every
+        # GET or HEAD request.
+        #
+        # For other methods, we need to know to bail out before request
+        # processing, especially for methods that modify server state (eg. PUT).
+        # We also would like to do so even for methods that don't, if those
+        # methods might be expensive to process.  We're assuming that GET and
+        # HEAD are not expensive.
+        #
+        if request.method not in ("GET", "HEAD"):
+            http.checkPreconditions(request)
+
+        super(StaticRenderMixin, self).checkPreconditions(request)
+
     def renderHTTP(self, request):
         """
         See L{iweb.IResource.renderHTTP}.
@@ -52,6 +74,8 @@
             response.headers.setHeader("allow", self.allowedMethods())
             return response
 
+        self.checkPreconditions(request)
+
         return method(request)
 
     def http_OPTIONS(self, request):
Index: twisted/web2/server.py
===================================================================
--- twisted/web2/server.py      (revision 15880)
+++ twisted/web2/server.py      (working copy)
@@ -40,9 +40,8 @@
 defaultHeadersFilter.handleErrors = True
 
 def preconditionfilter(request, response):
-    newresponse = http.checkPreconditions(request, response)
-    if newresponse is not None:
-        return newresponse
+    if request.method in ("GET", "HEAD"):
+        http.checkPreconditions(request, response)
     return response
 
 def doTrace(request):