diff --git a/OpenRA.Game/Traits/TraitsInterfaces.cs b/OpenRA.Game/Traits/TraitsInterfaces.cs
index 07d0fef2ca..5e76697ac1 100644
--- a/OpenRA.Game/Traits/TraitsInterfaces.cs
+++ b/OpenRA.Game/Traits/TraitsInterfaces.cs
@@ -205,7 +205,7 @@ namespace OpenRA.Traits
 	}
 
 	public interface IRenderModifier { IEnumerable<IRenderable> ModifyRender(Actor self, WorldRenderer wr, IEnumerable<IRenderable> r); }
-	public interface IDamageModifier { int GetDamageModifier(Actor attacker, DamageWarhead warhead); }
+	public interface IDamageModifier { int GetDamageModifier(Actor attacker, IWarhead warhead); }
 	public interface ISpeedModifier { int GetSpeedModifier(); }
 	public interface IFirepowerModifier { int GetFirepowerModifier(); }
 	public interface IReloadModifier { int GetReloadModifier(); }
diff --git a/OpenRA.Mods.Cnc/Traits/AttackPopupTurreted.cs b/OpenRA.Mods.Cnc/Traits/AttackPopupTurreted.cs
index 805874de89..15db5c91ef 100644
--- a/OpenRA.Mods.Cnc/Traits/AttackPopupTurreted.cs
+++ b/OpenRA.Mods.Cnc/Traits/AttackPopupTurreted.cs
@@ -9,7 +9,6 @@
 #endregion
 
 using System.Linq;
-using OpenRA.GameRules;
 using OpenRA.Mods.Common.Traits;
 using OpenRA.Traits;
 
@@ -101,7 +100,7 @@ namespace OpenRA.Mods.Cnc.Traits
 			}
 		}
 
-		public int GetDamageModifier(Actor attacker, DamageWarhead warhead)
+		public int GetDamageModifier(Actor attacker, IWarhead warhead)
 		{
 			return state == PopupState.Closed ? info.ClosedDamageMultiplier : 100;
 		}
diff --git a/OpenRA.Mods.Common/Traits/Infantry/TakeCover.cs b/OpenRA.Mods.Common/Traits/Infantry/TakeCover.cs
index 46e95ac595..b84b1ce5a4 100644
--- a/OpenRA.Mods.Common/Traits/Infantry/TakeCover.cs
+++ b/OpenRA.Mods.Common/Traits/Infantry/TakeCover.cs
@@ -10,7 +10,7 @@
 
 using System.Collections.Generic;
 using System.Linq;
-using OpenRA.GameRules;
+using OpenRA.Mods.Common.Warheads;
 using OpenRA.Traits;
 
 namespace OpenRA.Mods.Common.Traits
@@ -64,7 +64,8 @@ namespace OpenRA.Mods.Common.Traits
 
 		public void Damaged(Actor self, AttackInfo e)
 		{
-			if (e.Damage <= 0 || e.Warhead == null || !e.Warhead.DamageTypes.Any(x => info.DamageTriggers.Contains(x)))
+			var warhead = e.Warhead as DamageWarhead;
+			if (e.Damage <= 0 || warhead == null || !warhead.DamageTypes.Any(x => info.DamageTriggers.Contains(x)))
 				return;
 
 			if (!IsProne)
@@ -81,12 +82,16 @@ namespace OpenRA.Mods.Common.Traits
 				localOffset = WVec.Zero;
 		}
 
-		public int GetDamageModifier(Actor attacker, DamageWarhead warhead)
+		public int GetDamageModifier(Actor attacker, IWarhead warhead)
 		{
 			if (!IsProne)
 				return 100;
 
-			var modifierPercentages = info.DamageModifiers.Where(x => warhead.DamageTypes.Contains(x.Key)).Select(x => x.Value);
+			var damageWh = warhead as DamageWarhead;
+			if (damageWh == null)
+				return 100;
+
+			var modifierPercentages = info.DamageModifiers.Where(x => damageWh.DamageTypes.Contains(x.Key)).Select(x => x.Value);
 			return Util.ApplyPercentageModifiers(100, modifierPercentages);
 		}
 
diff --git a/OpenRA.Mods.Common/Traits/Infantry/TerrainModifiesDamage.cs b/OpenRA.Mods.Common/Traits/Infantry/TerrainModifiesDamage.cs
index a564f484de..cd4eeb4ca8 100644
--- a/OpenRA.Mods.Common/Traits/Infantry/TerrainModifiesDamage.cs
+++ b/OpenRA.Mods.Common/Traits/Infantry/TerrainModifiesDamage.cs
@@ -8,10 +8,9 @@
   */
  #endregion
 
-using System;
 using System.Collections.Generic;
 using System.Linq;
-using OpenRA.GameRules;
+using OpenRA.Mods.Common.Warheads;
 using OpenRA.Traits;
 
 namespace OpenRA.Mods.Common.Traits
@@ -42,6 +41,8 @@ namespace OpenRA.Mods.Common.Traits
 
 	public class TerrainModifiesDamage : IDamageModifier
 	{
+		const int FullDamage = 100;
+
 		public readonly TerrainModifiesDamageInfo Info;
 
 		readonly Actor self;
@@ -52,11 +53,11 @@ namespace OpenRA.Mods.Common.Traits
 			this.self = self;
 		}
 
-		public int GetDamageModifier(Actor attacker, DamageWarhead warhead)
+		public int GetDamageModifier(Actor attacker, IWarhead warhead)
 		{
-			var percent = 100;
-			if (attacker.Owner.IsAlliedWith(self.Owner) && (warhead != null && warhead.Damage < 0) && !Info.ModifyHealing)
-				return percent;
+			var damageWh = warhead as DamageWarhead;
+			if (attacker.Owner.IsAlliedWith(self.Owner) && (damageWh != null && damageWh.Damage < 0) && !Info.ModifyHealing)
+				return FullDamage;
 
 			var world = self.World;
 			var map = world.Map;
@@ -67,7 +68,7 @@ namespace OpenRA.Mods.Common.Traits
 			var terrainType = tileSet[tileSet.GetTerrainIndex(tiles[pos])].Type;
 
 			if (!Info.TerrainModifier.ContainsKey(terrainType))
-				return percent;
+				return FullDamage;
 
 			return Info.TerrainModifier[terrainType];
 		}
diff --git a/OpenRA.Mods.Common/Traits/Invulnerable.cs b/OpenRA.Mods.Common/Traits/Invulnerable.cs
index 8962b96fe7..996acb2dcc 100644
--- a/OpenRA.Mods.Common/Traits/Invulnerable.cs
+++ b/OpenRA.Mods.Common/Traits/Invulnerable.cs
@@ -8,7 +8,6 @@
  */
 #endregion
 
-using OpenRA.GameRules;
 using OpenRA.Traits;
 
 namespace OpenRA.Mods.Common.Traits
@@ -18,6 +17,6 @@ namespace OpenRA.Mods.Common.Traits
 
 	class Invulnerable : IDamageModifier
 	{
-		public int GetDamageModifier(Actor attacker, DamageWarhead warhead) { return 0; }
+		public int GetDamageModifier(Actor attacker, IWarhead warhead) { return 0; }
 	}
 }
diff --git a/OpenRA.Mods.Common/Traits/Upgrades/GainsStatUpgrades.cs b/OpenRA.Mods.Common/Traits/Upgrades/GainsStatUpgrades.cs
index 9aec86e9bb..313e9a175c 100644
--- a/OpenRA.Mods.Common/Traits/Upgrades/GainsStatUpgrades.cs
+++ b/OpenRA.Mods.Common/Traits/Upgrades/GainsStatUpgrades.cs
@@ -99,7 +99,7 @@ namespace OpenRA.Mods.Common.Traits
 				inaccuracyLevel = newLevel.Clamp(0, info.InaccuracyModifier.Length);
 		}
 
-		public int GetDamageModifier(Actor attacker, DamageWarhead warhead)
+		public int GetDamageModifier(Actor attacker, IWarhead warhead)
 		{
 			return damageLevel > 0 ? info.DamageModifier[damageLevel - 1] : 100;
 		}
diff --git a/OpenRA.Mods.RA/Traits/InvulnerabilityUpgrade.cs b/OpenRA.Mods.RA/Traits/InvulnerabilityUpgrade.cs
index d024cf196d..26b457fc61 100644
--- a/OpenRA.Mods.RA/Traits/InvulnerabilityUpgrade.cs
+++ b/OpenRA.Mods.RA/Traits/InvulnerabilityUpgrade.cs
@@ -8,7 +8,6 @@
  */
 #endregion
 
-using OpenRA.GameRules;
 using OpenRA.Mods.Common.Traits;
 using OpenRA.Traits;
 
@@ -24,7 +23,7 @@ namespace OpenRA.Mods.RA
 		public InvulnerabilityUpgrade(InvulnerabilityUpgradeInfo info)
 			: base(info) { }
 
-		public int GetDamageModifier(Actor attacker, DamageWarhead warhead)
+		public int GetDamageModifier(Actor attacker, IWarhead warhead)
 		{
 			return IsTraitDisabled ? 100 : 0;
 		}