diff --git a/OpenRA.Mods.Common/OpenRA.Mods.Common.csproj b/OpenRA.Mods.Common/OpenRA.Mods.Common.csproj
index c0938fdadc..93310b99ab 100644
--- a/OpenRA.Mods.Common/OpenRA.Mods.Common.csproj
+++ b/OpenRA.Mods.Common/OpenRA.Mods.Common.csproj
@@ -775,6 +775,7 @@
     <Compile Include="Traits\AutoCarryall.cs" />
     <Compile Include="Traits\World\CliffBackImpassabilityLayer.cs" />
     <Compile Include="Traits\Upgrades\GrantCondition.cs" />
+    <Compile Include="Traits\Upgrades\ExternalConditions.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <Target Name="AfterBuild">
diff --git a/OpenRA.Mods.Common/Traits/Upgrades/ExternalConditions.cs b/OpenRA.Mods.Common/Traits/Upgrades/ExternalConditions.cs
new file mode 100644
index 0000000000..c544a6c188
--- /dev/null
+++ b/OpenRA.Mods.Common/Traits/Upgrades/ExternalConditions.cs
@@ -0,0 +1,25 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2016 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using OpenRA.Traits;
+
+namespace OpenRA.Mods.Common.Traits
+{
+	[Desc("Lists conditions that are accepted from external sources (Lua, warheads, etc).",
+		"Externally granted conditions that aren't explicitly whitelisted will be silently ignored.")]
+	public class ExternalConditionsInfo : TraitInfo<ExternalConditions>
+	{
+		[UpgradeGrantedReference]
+		public readonly string[] Conditions = { };
+	}
+
+	public class ExternalConditions { }
+}
diff --git a/OpenRA.Mods.Common/Traits/Upgrades/UpgradeManager.cs b/OpenRA.Mods.Common/Traits/Upgrades/UpgradeManager.cs
index d7a07ef96e..b443593dce 100644
--- a/OpenRA.Mods.Common/Traits/Upgrades/UpgradeManager.cs
+++ b/OpenRA.Mods.Common/Traits/Upgrades/UpgradeManager.cs
@@ -24,6 +24,7 @@ namespace OpenRA.Mods.Common.Traits
 	{
 		/// <summary>Value used to represent an invalid token.</summary>
 		public static readonly int InvalidConditionToken = -1;
+		string[] externalConditions = { };
 
 		class TimedCondition
 		{
@@ -120,6 +121,12 @@ namespace OpenRA.Mods.Common.Traits
 			// Update all traits with their initial condition state
 			foreach (var consumer in allConsumers)
 				consumer.ConditionsChanged(self, readOnlyConditionCache);
+
+			// Build external condition whitelist
+			externalConditions = self.Info.TraitInfos<ExternalConditionsInfo>()
+				.SelectMany(t => t.Conditions)
+				.Distinct()
+				.ToArray();
 		}
 
 		void UpdateConditionState(Actor self, string condition, int token, bool isRevoke)
@@ -141,8 +148,12 @@ namespace OpenRA.Mods.Common.Traits
 
 		/// <summary>Grants a specified condition.</summary>
 		/// <returns>The token that is used to revoke this condition.</returns>
-		public int GrantCondition(Actor self, string condition)
+		/// <param name="external">Validate against the external condition whitelist.</param>
+		public int GrantCondition(Actor self, string condition, bool external = false)
 		{
+			if (external && !externalConditions.Contains(condition))
+				return InvalidConditionToken;
+
 			var token = nextToken++;
 			tokens.Add(token, condition);
 
@@ -155,7 +166,7 @@ namespace OpenRA.Mods.Common.Traits
 		}
 
 		/// <summary>Revokes a previously granted condition.</summary>
-		/// <returns>The invalid token ID</returns>
+		/// <returns>The invalid token ID.</returns>
 		/// <param name="token">The token ID returned by GrantCondition.</param>
 		public int RevokeCondition(Actor self, int token)
 		{
@@ -172,6 +183,15 @@ namespace OpenRA.Mods.Common.Traits
 			return InvalidConditionToken;
 		}
 
+		/// <summary>Returns true if the given external condition will have an effect on this actor.</summary>
+		public bool AcceptsExternalCondition(Actor self, string condition)
+		{
+			if (state == null)
+				throw new InvalidOperationException("AcceptsExternalCondition cannot be queried before the actor has been fully created.");
+
+			return externalConditions.Contains(condition) && !conditionCache[condition];
+		}
+
 		#region Shim methods for legacy upgrade granting code
 
 		void CheckCanManageConditions()