diff --git a/OpenRA.Mods.Common/Traits/Player/TechTree.cs b/OpenRA.Mods.Common/Traits/Player/TechTree.cs
index a95830432a..4b335630ed 100644
--- a/OpenRA.Mods.Common/Traits/Player/TechTree.cs
+++ b/OpenRA.Mods.Common/Traits/Player/TechTree.cs
@@ -9,6 +9,7 @@
  */
 #endregion
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using OpenRA.Primitives;
@@ -66,7 +67,7 @@ namespace OpenRA.Mods.Common.Traits
 		public bool HasPrerequisites(IEnumerable<string> prerequisites)
 		{
 			var ownedPrereqs = GatherOwnedPrerequisites(player);
-			return prerequisites.All(p => !(p.Replace("~", "").StartsWith("!")
+			return prerequisites.All(p => !(p.Replace("~", "").StartsWith("!", StringComparison.Ordinal)
 					^ !ownedPrereqs.ContainsKey(p.Replace("!", "").Replace("~", ""))));
 		}
 
@@ -134,7 +135,7 @@ namespace OpenRA.Mods.Common.Traits
 				foreach (var prereq in prerequisites)
 				{
 					var withoutTilde = prereq.Replace("~", "");
-					if (withoutTilde.StartsWith("!") ^ !ownedPrerequisites.ContainsKey(withoutTilde.Replace("!", "")))
+					if (withoutTilde.StartsWith("!", StringComparison.Ordinal) ^ !ownedPrerequisites.ContainsKey(withoutTilde.Replace("!", "")))
 						return false;
 				}
 
@@ -146,10 +147,10 @@ namespace OpenRA.Mods.Common.Traits
 				// PERF: Avoid LINQ.
 				foreach (var prereq in prerequisites)
 				{
-					if (!prereq.StartsWith("~"))
+					if (!prereq.StartsWith("~", StringComparison.Ordinal))
 						continue;
 					var withoutTilde = prereq.Replace("~", "");
-					if (withoutTilde.StartsWith("!") ^ !ownedPrerequisites.ContainsKey(withoutTilde.Replace("!", "")))
+					if (withoutTilde.StartsWith("!", StringComparison.Ordinal) ^ !ownedPrerequisites.ContainsKey(withoutTilde.Replace("!", "")))
 						return true;
 				}