diff -Nru apt-0.9.7.5ubuntu5.4/apt-pkg/acquire-worker.cc apt-0.9.7.5ubuntu5.5/apt-pkg/acquire-worker.cc
--- apt-0.9.7.5ubuntu5.4/apt-pkg/acquire-worker.cc	2013-08-21 12:49:35.000000000 -0500
+++ apt-0.9.7.5ubuntu5.5/apt-pkg/acquire-worker.cc	2013-08-21 12:57:50.000000000 -0500
@@ -305,7 +305,15 @@
 	    
 	    OwnerQ->ItemDone(Itm);
 	    unsigned long long const ServerSize = strtoull(LookupTag(Message,"Size","0").c_str(), NULL, 10);
-	    if (TotalSize != 0 && ServerSize != TotalSize)
+	    bool isHit = StringToBool(LookupTag(Message,"IMS-Hit"),false) ||
+	                 StringToBool(LookupTag(Message,"Alt-IMS-Hit"),false);
+	    // Using the https method the server might return 200, but the
+	    // If-Modified-Since condition is not satsified, libcurl will
+	    // discard the download. In this case, however, TotalSize will be
+	    // set to the actual size of the file, while ServerSize will be set
+	    // to 0. Therefore, if the item is marked as a hit and the
+	    // downloaded size (ServerSize) is 0, we ignore TotalSize.
+	    if (TotalSize != 0 && (!isHit || ServerSize != 0) && ServerSize != TotalSize)
 	       _error->Warning("Size of file %s is not what the server reported %s %llu",
 			       Owner->DestFile.c_str(), LookupTag(Message,"Size","0").c_str(),TotalSize);
 
@@ -332,8 +340,7 @@
 	    // Log that we are done
 	    if (Log != 0)
 	    {
-	       if (StringToBool(LookupTag(Message,"IMS-Hit"),false) == true ||
-		   StringToBool(LookupTag(Message,"Alt-IMS-Hit"),false) == true)
+	       if (isHit)
 	       {
 		  /* Hide 'hits' for local only sources - we also manage to
 		     hide gets */
diff -Nru apt-0.9.7.5ubuntu5.4/debian/changelog apt-0.9.7.5ubuntu5.5/debian/changelog
--- apt-0.9.7.5ubuntu5.4/debian/changelog	2013-08-21 12:49:35.000000000 -0500
+++ apt-0.9.7.5ubuntu5.5/debian/changelog	2013-08-21 13:14:24.000000000 -0500
@@ -1,3 +1,9 @@
+apt (0.9.7.5ubuntu5.5) quantal; urgency=low
+
+  * If-modified-since unhandled case causes apt lists corruption (LP: #1179781) 
+
+ -- Dave Chiluk <chiluk@canonical.com>  Wed, 21 Aug 2013 13:14:06 -0500
+
 apt (0.9.7.5ubuntu5.4) quantal-security; urgency=low
 
   * SECURITY UPDATE: InRelease verification bypass
diff -Nru apt-0.9.7.5ubuntu5.4/debian/control apt-0.9.7.5ubuntu5.5/debian/control
--- apt-0.9.7.5ubuntu5.4/debian/control	2013-08-21 12:49:35.000000000 -0500
+++ apt-0.9.7.5ubuntu5.5/debian/control	2013-08-30 14:04:24.000000000 -0500
@@ -120,7 +120,7 @@
 
 Package: apt-transport-https
 Architecture: any
-Depends: ${shlibs:Depends}, ${misc:Depends}
+Depends: ${shlibs:Depends}, ${misc:Depends}, libcurl3-gnutls (>= 7.27.0-1ubuntu1.4)
 Priority: optional
 Description: https download transport for APT
  This package enables the usage of 'deb https://foo distro main' lines
diff -Nru apt-0.9.7.5ubuntu5.4/methods/https.cc apt-0.9.7.5ubuntu5.5/methods/https.cc
--- apt-0.9.7.5ubuntu5.4/methods/https.cc	2013-08-21 12:49:35.000000000 -0500
+++ apt-0.9.7.5ubuntu5.5/methods/https.cc	2013-08-21 12:57:50.000000000 -0500
@@ -285,6 +285,11 @@
    long curl_servdate;
    curl_easy_getinfo(curl, CURLINFO_FILETIME, &curl_servdate);
 
+   // If the server returns 200 OK but the If-Modified-Since condition is not
+   // met, CURLINFO_CONDITION_UNMET will be set to 1
+   long curl_condition_unmet = 0;
+   curl_easy_getinfo(curl, CURLINFO_CONDITION_UNMET, &curl_condition_unmet);
+
    File->Close();
 
    // cleanup
@@ -312,7 +317,7 @@
       Res.Filename = File->Name();
       Res.LastModified = Buf.st_mtime;
       Res.IMSHit = false;
-      if (curl_responsecode == 304)
+      if (curl_responsecode == 304 || curl_condition_unmet)
       {
 	 unlink(File->Name().c_str());
 	 Res.IMSHit = true;