diff --git a/plugins/buildingplan-lib.h b/plugins/buildingplan-lib.h
index 7ec0c41d4..6975960d2 100644
--- a/plugins/buildingplan-lib.h
+++ b/plugins/buildingplan-lib.h
@@ -114,7 +114,9 @@ struct ItemFilter
     bool decorated_only;
 
     ItemFilter() : min_quality(df::item_quality::Ordinary), decorated_only(false), valid(true)
-    {    }
+    {
+        clear(); // mat_mask is not cleared by default (see issue #1047)
+    }
 
     bool matchesMask(DFHack::MaterialInfo &mat);
 
diff --git a/plugins/lua/stockflow.lua b/plugins/lua/stockflow.lua
index 6027bb455..dd83e65d9 100644
--- a/plugins/lua/stockflow.lua
+++ b/plugins/lua/stockflow.lua
@@ -1135,8 +1135,7 @@ function check_stockpiles(verbose)
         if trigger and trigger.divisor then
             local reaction = spec.entry.ints[entry_ints.order_number]
             local filled, empty = check_pile(spec.stockpile, verbose)
-            local amount = trigger.filled and filled or empty
-            amount = (amount - (amount % trigger.divisor)) / trigger.divisor
+            local amount = math.floor((trigger.filled and filled or empty) / trigger.divisor)
             result[reaction] = (result[reaction] or 0) + amount
         end
     end
diff --git a/plugins/workflow.cpp b/plugins/workflow.cpp
index 55f1dc504..f8f9e8231 100644
--- a/plugins/workflow.cpp
+++ b/plugins/workflow.cpp
@@ -357,7 +357,9 @@ public:
         : is_craft(false), min_quality(item_quality::Ordinary), is_local(false),
           weight(0), item_amount(0), item_count(0), item_inuse_amount(0), item_inuse_count(0),
           is_active(false), cant_resume_reported(false), low_stock_reported(-1)
-    {}
+    {
+        mat_mask.whole = 0; // see https://github.com/DFHack/dfhack/issues/1047
+    }
 
     int goalCount() { return config.ival(0); }
     void setGoalCount(int v) { config.ival(0) = v; }