diff --git a/OpenRA.Mods.Common/Traits/Player/BaseAttackNotifier.cs b/OpenRA.Mods.Common/Traits/Player/BaseAttackNotifier.cs
index 280014a5f4..4c61c0e451 100644
--- a/OpenRA.Mods.Common/Traits/Player/BaseAttackNotifier.cs
+++ b/OpenRA.Mods.Common/Traits/Player/BaseAttackNotifier.cs
@@ -32,7 +32,7 @@ namespace OpenRA.Mods.Common.Traits
 		public readonly string Notification = "BaseAttack";
 
 		[Desc("Text notification to display.")]
-		public string TextNotification = null;
+		public readonly string TextNotification = null;
 
 		[NotificationReference("Speech")]
 		[Desc("Speech notification to play to allies when under attack.",
@@ -40,7 +40,7 @@ namespace OpenRA.Mods.Common.Traits
 		public readonly string AllyNotification = null;
 
 		[Desc("Text notification to display to allies when under attack.")]
-		public string AllyTextNotification = null;
+		public readonly string AllyTextNotification = null;
 
 		public override object Create(ActorInitializer init) { return new BaseAttackNotifier(init.Self, this); }
 	}
diff --git a/OpenRA.Mods.Common/Traits/Player/HarvesterAttackNotifier.cs b/OpenRA.Mods.Common/Traits/Player/HarvesterAttackNotifier.cs
index bf0f264791..ccd2d4c753 100644
--- a/OpenRA.Mods.Common/Traits/Player/HarvesterAttackNotifier.cs
+++ b/OpenRA.Mods.Common/Traits/Player/HarvesterAttackNotifier.cs
@@ -32,7 +32,7 @@ namespace OpenRA.Mods.Common.Traits
 		public readonly string Notification = "HarvesterAttack";
 
 		[Desc("Text notification to display.")]
-		public string TextNotification = null;
+		public readonly string TextNotification = null;
 
 		public override object Create(ActorInitializer init) { return new HarvesterAttackNotifier(init.Self, this); }
 	}
diff --git a/OpenRA.Mods.Common/Traits/Sellable.cs b/OpenRA.Mods.Common/Traits/Sellable.cs
index 12158fa9fd..be484667cf 100644
--- a/OpenRA.Mods.Common/Traits/Sellable.cs
+++ b/OpenRA.Mods.Common/Traits/Sellable.cs
@@ -31,7 +31,7 @@ namespace OpenRA.Mods.Common.Traits
 		public readonly string Notification = null;
 
 		[Desc("Text notification to display.")]
-		public string TextNotification = null;
+		public readonly string TextNotification = null;
 
 		[Desc("Whether to show the cash tick indicators rising from the actor.")]
 		public readonly bool ShowTicks = true;