diff --git a/.editorconfig b/.editorconfig
index 2a1e9b280f..df08541619 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -866,6 +866,9 @@ dotnet_diagnostic.CA1865.severity = suggestion # TODO: Change to warning once us
 dotnet_diagnostic.CA1866.severity = suggestion # TODO: Change to warning once using .NET 8 or later.
 dotnet_diagnostic.CA1867.severity = suggestion # TODO: Change to warning once using .NET 8 or later.
 
+# Unnecessary call to 'Contains' for sets.
+dotnet_diagnostic.CA1868.severity = suggestion # TODO: Change to warning once using .NET 8 or later.
+
 # Cache and reuse 'JsonSerializerOptions' instances.
 dotnet_diagnostic.CA1869.severity = suggestion # TODO: Change to warning once using .NET 8 or later.
 
diff --git a/OpenRA.Game/FileSystem/FileSystem.cs b/OpenRA.Game/FileSystem/FileSystem.cs
index 74fd728216..f6518ee173 100644
--- a/OpenRA.Game/FileSystem/FileSystem.cs
+++ b/OpenRA.Game/FileSystem/FileSystem.cs
@@ -159,9 +159,7 @@ namespace OpenRA.FileSystem
 					explicitMounts.Remove(key);
 
 				// Mod packages aren't owned by us, so we shouldn't dispose them
-				if (modPackages.Contains(package))
-					modPackages.Remove(package);
-				else
+				if (!modPackages.Remove(package))
 					package.Dispose();
 			}
 			else
diff --git a/OpenRA.Game/Traits/World/ScreenMap.cs b/OpenRA.Game/Traits/World/ScreenMap.cs
index 34a445846f..46e3c2b092 100644
--- a/OpenRA.Game/Traits/World/ScreenMap.cs
+++ b/OpenRA.Game/Traits/World/ScreenMap.cs
@@ -85,8 +85,7 @@ namespace OpenRA.Traits
 
 		public void AddOrUpdate(Player viewer, FrozenActor fa)
 		{
-			if (removeFrozenActors[viewer].Contains(fa))
-				removeFrozenActors[viewer].Remove(fa);
+			removeFrozenActors[viewer].Remove(fa);
 
 			addOrUpdateFrozenActors[viewer].Add(fa);
 		}
@@ -98,8 +97,7 @@ namespace OpenRA.Traits
 
 		public void AddOrUpdate(Actor a)
 		{
-			if (removeActors.Contains(a))
-				removeActors.Remove(a);
+			removeActors.Remove(a);
 
 			addOrUpdateActors.Add(a);
 		}
diff --git a/OpenRA.Mods.Common/ServerTraits/LobbyCommands.cs b/OpenRA.Mods.Common/ServerTraits/LobbyCommands.cs
index 0d701607d8..8a8097f151 100644
--- a/OpenRA.Mods.Common/ServerTraits/LobbyCommands.cs
+++ b/OpenRA.Mods.Common/ServerTraits/LobbyCommands.cs
@@ -1163,9 +1163,7 @@ namespace OpenRA.Mods.Common.Server
 
 			// Clearing an empty spawn point prevents it from being selected
 			// Clearing a disabled spawn restores it for use
-			if (!server.LobbyInfo.DisabledSpawnPoints.Contains(spawnPoint))
-				server.LobbyInfo.DisabledSpawnPoints.Add(spawnPoint);
-			else
+			if (!server.LobbyInfo.DisabledSpawnPoints.Add(spawnPoint))
 				server.LobbyInfo.DisabledSpawnPoints.Remove(spawnPoint);
 
 			server.SyncLobbyInfo();
diff --git a/OpenRA.Mods.Common/Traits/DockHost.cs b/OpenRA.Mods.Common/Traits/DockHost.cs
index 2c00b156f1..24f0460aa6 100644
--- a/OpenRA.Mods.Common/Traits/DockHost.cs
+++ b/OpenRA.Mods.Common/Traits/DockHost.cs
@@ -104,11 +104,8 @@ namespace OpenRA.Mods.Common.Traits
 
 		public virtual void Unreserve(DockClientManager client)
 		{
-			if (ReservedDockClients.Contains(client))
-			{
-				ReservedDockClients.Remove(client);
+			if (ReservedDockClients.Remove(client))
 				client.UnreserveHost();
-			}
 		}
 
 		public virtual void OnDockStarted(Actor self, Actor clientActor, DockClientManager client)