diff -r f500f32cfc51 -r 3a8eb6336012 src/mem/cache/cache.cc
--- a/src/mem/cache/cache.cc	Mon Dec 19 01:09:06 2016 -0600
+++ b/src/mem/cache/cache.cc	Mon Dec 19 12:40:29 2016 -0600
@@ -2036,7 +2036,8 @@
 
         // if we are returning a writable and dirty (Modified) line,
         // we should be invalidating the line
-        panic_if(!invalidate && !pkt->hasSharers(),
+        panic_if(!invalidate && !pkt->hasSharers() &&
+                                !pkt->req->isUncacheable(),
                  "%s is passing a Modified line through %s, "
                  "but keeping the block", name(), pkt->print());