diff --git a/frontend/document/doccache.lua b/frontend/document/doccache.lua
index 0cc7c2be8..95b9961b6 100644
--- a/frontend/document/doccache.lua
+++ b/frontend/document/doccache.lua
@@ -15,7 +15,8 @@ local DHINTCOUNT = G_defaults:readSetting("DHINTCOUNT")
 local function calcCacheMemSize()
     local min = G_defaults:readSetting("DGLOBAL_CACHE_SIZE_MINIMUM")
     local max = G_defaults:readSetting("DGLOBAL_CACHE_SIZE_MAXIMUM")
-    local calc = util.calcFreeMem() * (G_defaults:readSetting("DGLOBAL_CACHE_FREE_PROPORTION") or 0)
+    local memfree, _ = util.calcFreeMem() or 0, 0
+    local calc = memfree * G_defaults:readSetting("DGLOBAL_CACHE_FREE_PROPORTION")
     return math.min(max, math.max(min, calc))
 end
 local doccache_size = calcCacheMemSize()