diff --git a/OpenRA.Mods.Common/Lint/CheckActorReferences.cs b/OpenRA.Mods.Common/Lint/CheckActorReferences.cs
index 34e8f39af4..b025b6ff1a 100644
--- a/OpenRA.Mods.Common/Lint/CheckActorReferences.cs
+++ b/OpenRA.Mods.Common/Lint/CheckActorReferences.cs
@@ -92,7 +92,7 @@ namespace OpenRA.Mods.Common.Lint
 				if (value == null)
 					continue;
 
-				if (!dict.ContainsKey(value.ToLower()))
+				if (!dict.ContainsKey(value.ToLowerInvariant()))
 					emitError("{0}.{1}.{2}: Missing weapon `{3}`."
 						.F(actorInfo.Name, traitInfo.GetType().Name, fieldInfo.Name, value));
 			}
@@ -110,7 +110,7 @@ namespace OpenRA.Mods.Common.Lint
 				if (value == null)
 					continue;
 
-				if (!dict.ContainsKey(value.ToLower()))
+				if (!dict.ContainsKey(value.ToLowerInvariant()))
 					emitError("{0}.{1}.{2}: Missing voice `{3}`."
 						.F(actorInfo.Name, traitInfo.GetType().Name, fieldInfo.Name, value));
 			}
diff --git a/OpenRA.Mods.Common/Traits/Buildings/FreeActorWithDelivery.cs b/OpenRA.Mods.Common/Traits/Buildings/FreeActorWithDelivery.cs
index 20a5b39343..4e2b8d3abe 100644
--- a/OpenRA.Mods.Common/Traits/Buildings/FreeActorWithDelivery.cs
+++ b/OpenRA.Mods.Common/Traits/Buildings/FreeActorWithDelivery.cs
@@ -88,7 +88,7 @@ namespace OpenRA.Mods.Common.Traits
 			var initialFacing = self.World.Map.FacingBetween(location, self.Location, 0);
 
 			// If aircraft, spawn at cruise altitude
-			var aircraftInfo = self.World.Map.Rules.Actors[deliveringActorName.ToLower()].TraitInfoOrDefault<AircraftInfo>();
+			var aircraftInfo = self.World.Map.Rules.Actors[deliveringActorName.ToLowerInvariant()].TraitInfoOrDefault<AircraftInfo>();
 			if (aircraftInfo != null)
 				spawn += new WVec(0, 0, aircraftInfo.CruiseAltitude.Length);
 
diff --git a/OpenRA.Mods.Common/UtilityCommands/ImportLegacyMapCommand.cs b/OpenRA.Mods.Common/UtilityCommands/ImportLegacyMapCommand.cs
index 7ee01c09e8..8eaacf3a69 100644
--- a/OpenRA.Mods.Common/UtilityCommands/ImportLegacyMapCommand.cs
+++ b/OpenRA.Mods.Common/UtilityCommands/ImportLegacyMapCommand.cs
@@ -182,19 +182,19 @@ namespace OpenRA.Mods.Common.UtilityCommands
 					switch (s.Key)
 					{
 					case "Intro":
-						videos.Add(new MiniYamlNode("BackgroundVideo", s.Value.ToLower() + ".vqa"));
+						videos.Add(new MiniYamlNode("BackgroundVideo", s.Value.ToLowerInvariant() + ".vqa"));
 						break;
 					case "Brief":
-						videos.Add(new MiniYamlNode("BriefingVideo", s.Value.ToLower() + ".vqa"));
+						videos.Add(new MiniYamlNode("BriefingVideo", s.Value.ToLowerInvariant() + ".vqa"));
 						break;
 					case "Action":
-						videos.Add(new MiniYamlNode("StartVideo", s.Value.ToLower() + ".vqa"));
+						videos.Add(new MiniYamlNode("StartVideo", s.Value.ToLowerInvariant() + ".vqa"));
 						break;
 					case "Win":
-						videos.Add(new MiniYamlNode("WinVideo", s.Value.ToLower() + ".vqa"));
+						videos.Add(new MiniYamlNode("WinVideo", s.Value.ToLowerInvariant() + ".vqa"));
 						break;
 					case "Lose":
-						videos.Add(new MiniYamlNode("LossVideo", s.Value.ToLower() + ".vqa"));
+						videos.Add(new MiniYamlNode("LossVideo", s.Value.ToLowerInvariant() + ".vqa"));
 						break;
 					}
 				}
diff --git a/OpenRA.Mods.D2k/UtilityCommands/D2kMapImporter.cs b/OpenRA.Mods.D2k/UtilityCommands/D2kMapImporter.cs
index 3f98074fe0..c190fd4900 100644
--- a/OpenRA.Mods.D2k/UtilityCommands/D2kMapImporter.cs
+++ b/OpenRA.Mods.D2k/UtilityCommands/D2kMapImporter.cs
@@ -322,7 +322,7 @@ namespace OpenRA.Mods.D2k.UtilityCommands
 			// Get all templates from the tileset YAML file that have at least one frame and an Image property corresponding to the requested tileset
 			// Each frame is a tile from the Dune 2000 tileset files, with the Frame ID being the index of the tile in the original file
 			tileSetsFromYaml = tileSet.Templates.Where(t => t.Value.Frames != null
-				&& t.Value.Images[0].ToLower() == tilesetName.ToLower()).Select(ts => ts.Value).ToList();
+				&& t.Value.Images[0].ToLowerInvariant() == tilesetName.ToLowerInvariant()).Select(ts => ts.Value).ToList();
 
 			var players = new MapPlayers(map.Rules, playerCount);
 			map.PlayerDefinitions = players.ToMiniYaml();
@@ -350,7 +350,7 @@ namespace OpenRA.Mods.D2k.UtilityCommands
 				if (ActorDataByActorCode.ContainsKey(tileSpecialInfo))
 				{
 					var kvp = ActorDataByActorCode[tileSpecialInfo];
-					if (!rules.Actors.ContainsKey(kvp.First.ToLower()))
+					if (!rules.Actors.ContainsKey(kvp.First.ToLowerInvariant()))
 						throw new InvalidOperationException("Actor with name {0} could not be found in the rules YAML file!".F(kvp.First));
 
 					var a = new ActorReference(kvp.First)
@@ -380,7 +380,7 @@ namespace OpenRA.Mods.D2k.UtilityCommands
 		TerrainTile GetTile(int tileIndex)
 		{
 			// Some tiles are duplicates of other tiles, just on a different tileset
-			if (tilesetName.ToLower() == "bloxbgbs.r8")
+			if (tilesetName.ToLowerInvariant() == "bloxbgbs.r8")
 			{
 				if (tileIndex == 355)
 					return new TerrainTile(441, 0);
@@ -389,7 +389,7 @@ namespace OpenRA.Mods.D2k.UtilityCommands
 					return new TerrainTile(442, 0);
 			}
 
-			if (tilesetName.ToLower() == "bloxtree.r8")
+			if (tilesetName.ToLowerInvariant() == "bloxtree.r8")
 			{
 				var indices = new[] { 683, 684, 685, 706, 703, 704, 705, 726, 723, 724, 725, 746, 743, 744, 745, 747 };
 				for (var i = 0; i < 16; i++)
@@ -410,7 +410,7 @@ namespace OpenRA.Mods.D2k.UtilityCommands
 					return new TerrainTile(215, 0);
 			}
 
-			if (tilesetName.ToLower() == "bloxwast.r8")
+			if (tilesetName.ToLowerInvariant() == "bloxwast.r8")
 			{
 				if (tileIndex == 342)
 					return new TerrainTile(250, 0);