diff --git a/dom0/qmemman/qmemman_algo.py b/dom0/qmemman/qmemman_algo.py
index 22c3feb5..e64c76de 100755
--- a/dom0/qmemman/qmemman_algo.py
+++ b/dom0/qmemman/qmemman_algo.py
@@ -60,7 +60,7 @@ def prefmem(domain):
     CACHE_FACTOR = 1.3
 #dom0 is special, as it must have large cache, for vbds. Thus, give it a special boost
     if domain.id == '0':
-        return domain.mem_used*CACHE_FACTOR + 350*1024*1024
+        return min(domain.mem_used*CACHE_FACTOR + 350*1024*1024, domain.memory_maximum)
     return min(domain.mem_used*CACHE_FACTOR, domain.memory_maximum)
 
 def memory_needed(domain):