diff --git a/cont/LuaUI/callins.lua b/cont/LuaUI/callins.lua
index e71f7bd0f7..a7e5bb947b 100644
--- a/cont/LuaUI/callins.lua
+++ b/cont/LuaUI/callins.lua
@@ -44,6 +44,7 @@ CallInsList = {
 	"UnitFinished",
 	"UnitFromFactory",
 	"UnitReverseBuilt",
+	"UnitConstructionDecayed",
 	"UnitDestroyed",
 	"RenderUnitDestroyed",
 	"UnitTaken",
diff --git a/cont/LuaUI/widgets.lua b/cont/LuaUI/widgets.lua
index 510137cd76..d9f9ea6152 100644
--- a/cont/LuaUI/widgets.lua
+++ b/cont/LuaUI/widgets.lua
@@ -123,6 +123,7 @@ local flexCallIns = {
   'UnitFinished',
   'UnitFromFactory',
   'UnitReverseBuilt',
+  'UnitConstructionDecayed',
   'UnitDestroyed',
   'RenderUnitDestroyed',
   'UnitTaken',
@@ -1853,6 +1854,14 @@ function widgetHandler:UnitReverseBuilt(unitID, unitDefID, unitTeam)
 end
 
 
+function widgetHandler:UnitConstructionDecayed(unitID, unitDefID, unitTeam, part)
+  for _,w in ipairs(self.UnitConstructionDecayedList) do
+    w:UnitConstructionDecayed(unitID, unitDefID, unitTeam, part)
+  end
+  return
+end
+
+
 function widgetHandler:UnitDestroyed(unitID, unitDefID, unitTeam)
   for _,w in ipairs(self.UnitDestroyedList) do
     w:UnitDestroyed(unitID, unitDefID, unitTeam)
diff --git a/cont/base/springcontent/LuaGadgets/callins.lua b/cont/base/springcontent/LuaGadgets/callins.lua
index 63061b813f..e820e39f8f 100644
--- a/cont/base/springcontent/LuaGadgets/callins.lua
+++ b/cont/base/springcontent/LuaGadgets/callins.lua
@@ -49,6 +49,7 @@ CALLIN_LIST = {
 	"UnitFinished",
 	"UnitFromFactory",
 	"UnitReverseBuilt",
+	"UnitConstructionDecayed",
 	"UnitDestroyed",
 	"RenderUnitDestroyed",
 	"UnitExperience",
diff --git a/cont/base/springcontent/LuaGadgets/gadgets.lua b/cont/base/springcontent/LuaGadgets/gadgets.lua
index 0f0ccc116c..0ae8ecf66f 100644
--- a/cont/base/springcontent/LuaGadgets/gadgets.lua
+++ b/cont/base/springcontent/LuaGadgets/gadgets.lua
@@ -1411,6 +1411,13 @@ function gadgetHandler:UnitReverseBuilt(unitID, unitDefID, unitTeam)
 end
 
 
+function gadgetHandler:UnitConstructionDecayed(unitID, unitDefID, unitTeam, part)
+  for _,g in r_ipairs(self.UnitConstructionDecayedList) do
+    g:UnitConstructionDecayed(unitID, unitDefID, unitTeam, part)
+  end
+end
+
+
 function gadgetHandler:UnitDestroyed(
   unitID,     unitDefID,     unitTeam,
   attackerID, attackerDefID, attackerTeam
diff --git a/rts/Lua/LuaHandle.cpp b/rts/Lua/LuaHandle.cpp
index ae66c3f6ff..e1b9a7718d 100644
--- a/rts/Lua/LuaHandle.cpp
+++ b/rts/Lua/LuaHandle.cpp
@@ -1078,6 +1078,35 @@ void CLuaHandle::UnitReverseBuilt(const CUnit* unit)
 }
 
 
+/*** Called when a unit being built starts decaying.
+ *
+ * @function UnitConstructionDecayed
+ * @number unitID
+ * @number unitDefID
+ * @number unitTeam
+ * @number part
+ */
+void CLuaHandle::UnitConstructionDecayed(const CUnit* unit, float part)
+{
+	RECOIL_DETAILED_TRACY_ZONE;
+	LUA_CALL_IN_CHECK(L);
+	luaL_checkstack(L, 7, __func__);
+	const LuaUtils::ScopedDebugTraceBack traceBack(L);
+
+	static const LuaHashString cmdStr(__func__);
+	if (!cmdStr.GetGlobalFunc(L))
+		return;
+
+	lua_pushnumber(L, unit->id);
+	lua_pushnumber(L, unit->unitDef->id);
+	lua_pushnumber(L, unit->team);
+	lua_pushnumber(L, part);
+
+	// call the routine
+	RunCallInTraceback(L, cmdStr, 4, 0, traceBack.GetErrFuncIdx(), false);
+}
+
+
 /*** Called when a unit is destroyed.
  *
  * @function UnitDestroyed
diff --git a/rts/Lua/LuaHandle.h b/rts/Lua/LuaHandle.h
index c2979880d2..cb0e1b7300 100644
--- a/rts/Lua/LuaHandle.h
+++ b/rts/Lua/LuaHandle.h
@@ -126,6 +126,7 @@ class CLuaHandle : public CEventClient
 		void UnitFinished(const CUnit* unit) override;
 		void UnitFromFactory(const CUnit* unit, const CUnit* factory, bool userOrders) override;
 		void UnitReverseBuilt(const CUnit* unit) override;
+		void UnitConstructionDecayed(const CUnit* unit, float part) override;
 		void UnitDestroyed(const CUnit* unit, const CUnit* attacker) override;
 		void UnitTaken(const CUnit* unit, int oldTeam, int newTeam) override;
 		void UnitGiven(const CUnit* unit, int oldTeam, int newTeam) override;
diff --git a/rts/Sim/Units/Unit.cpp b/rts/Sim/Units/Unit.cpp
index a569cb22fa..1a45b51d28 100644
--- a/rts/Sim/Units/Unit.cpp
+++ b/rts/Sim/Units/Unit.cpp
@@ -1013,6 +1013,8 @@ void CUnit::SlowUpdate()
 
 			AddMetal(cost.metal * buildDecay, false);
 
+			eventHandler.UnitConstructionDecayed(this, buildDecay);
+
 			if (health <= 0.0f || buildProgress <= 0.0f)
 				KillUnit(nullptr, false, true);
 		}
diff --git a/rts/System/EventClient.h b/rts/System/EventClient.h
index 88a570467d..33f99e5474 100644
--- a/rts/System/EventClient.h
+++ b/rts/System/EventClient.h
@@ -126,6 +126,7 @@ class CEventClient
 		virtual void UnitCreated(const CUnit* unit, const CUnit* builder) {}
 		virtual void UnitFinished(const CUnit* unit) {}
 		virtual void UnitReverseBuilt(const CUnit* unit) {}
+		virtual void UnitConstructionDecayed(const CUnit* unit, float part) {}
 		virtual void UnitFromFactory(const CUnit* unit, const CUnit* factory, bool userOrders) {}
 		virtual void UnitDestroyed(const CUnit* unit, const CUnit* attacker) {}
 		virtual void UnitTaken(const CUnit* unit, int oldTeam, int newTeam) {}
diff --git a/rts/System/EventHandler.h b/rts/System/EventHandler.h
index eb0a924718..f5a2743acf 100644
--- a/rts/System/EventHandler.h
+++ b/rts/System/EventHandler.h
@@ -65,6 +65,7 @@ class CEventHandler
 		void UnitCreated(const CUnit* unit, const CUnit* builder);
 		void UnitFinished(const CUnit* unit);
 		void UnitReverseBuilt(const CUnit* unit);
+		void UnitConstructionDecayed(const CUnit* unit, float part);
 		void UnitFromFactory(const CUnit* unit, const CUnit* factory, bool userOrders);
 		void UnitDestroyed(const CUnit* unit, const CUnit* attacker);
 		void UnitTaken(const CUnit* unit, int oldTeam, int newTeam);
@@ -463,6 +464,11 @@ UNIT_CALLIN_LOS_PARAM(LeftRadar)
 UNIT_CALLIN_LOS_PARAM(LeftLos)
 
 
+inline void CEventHandler::UnitConstructionDecayed(const CUnit* unit,
+                                                   float part)
+{
+	ITERATE_UNIT_ALLYTEAM_EVENTCLIENTLIST(UnitConstructionDecayed, unit, part)
+}
 
 inline void CEventHandler::UnitFromFactory(const CUnit* unit,
                                                const CUnit* factory,
diff --git a/rts/System/Events.def b/rts/System/Events.def
index d4e4361018..0120eab369 100644
--- a/rts/System/Events.def
+++ b/rts/System/Events.def
@@ -37,13 +37,14 @@
 	SETUP_EVENT(PlayerAdded,   MANAGED_BIT | UNSYNCED_BIT)
 	SETUP_EVENT(PlayerRemoved, MANAGED_BIT | UNSYNCED_BIT)
 
-	SETUP_EVENT(UnitCreated,      MANAGED_BIT)
-	SETUP_EVENT(UnitFinished,     MANAGED_BIT)
-	SETUP_EVENT(UnitFromFactory,  MANAGED_BIT)
-	SETUP_EVENT(UnitReverseBuilt, MANAGED_BIT)
-	SETUP_EVENT(UnitDestroyed,    MANAGED_BIT)
-	SETUP_EVENT(UnitTaken,        MANAGED_BIT)
-	SETUP_EVENT(UnitGiven,        MANAGED_BIT)
+	SETUP_EVENT(UnitCreated,             MANAGED_BIT)
+	SETUP_EVENT(UnitFinished,            MANAGED_BIT)
+	SETUP_EVENT(UnitFromFactory,         MANAGED_BIT)
+	SETUP_EVENT(UnitReverseBuilt,        MANAGED_BIT)
+	SETUP_EVENT(UnitConstructionDecayed, MANAGED_BIT)
+	SETUP_EVENT(UnitDestroyed,           MANAGED_BIT)
+	SETUP_EVENT(UnitTaken,               MANAGED_BIT)
+	SETUP_EVENT(UnitGiven,               MANAGED_BIT)
 
 	SETUP_EVENT(UnitIdle,       MANAGED_BIT)
 	SETUP_EVENT(UnitCommand,    MANAGED_BIT)