diff --git a/OpenRA.Game/OpenRA.Game.csproj b/OpenRA.Game/OpenRA.Game.csproj
index 3dda479609..e6c0d0354d 100644
--- a/OpenRA.Game/OpenRA.Game.csproj
+++ b/OpenRA.Game/OpenRA.Game.csproj
@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Library</OutputType>
-    <TargetFramework>netstandard2.1</TargetFramework>
+    <TargetFramework Condition="'$(Mono)' == ''">net5.0</TargetFramework>
+    <TargetFramework Condition="'$(Mono)' != ''">netstandard2.1</TargetFramework>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Optimize>true</Optimize>
     <UseVSHostingProcess>false</UseVSHostingProcess>
diff --git a/OpenRA.Game/Traits/ActivityUtils.cs b/OpenRA.Game/Traits/ActivityUtils.cs
index 425f54d38c..11b324df6e 100644
--- a/OpenRA.Game/Traits/ActivityUtils.cs
+++ b/OpenRA.Game/Traits/ActivityUtils.cs
@@ -12,6 +12,7 @@
 using System.Diagnostics;
 using OpenRA.Activities;
 using OpenRA.Support;
+using Activity = OpenRA.Activities.Activity;
 
 namespace OpenRA.Traits
 {
diff --git a/OpenRA.Mods.Cnc/OpenRA.Mods.Cnc.csproj b/OpenRA.Mods.Cnc/OpenRA.Mods.Cnc.csproj
index ff20634794..ac56d233cc 100644
--- a/OpenRA.Mods.Cnc/OpenRA.Mods.Cnc.csproj
+++ b/OpenRA.Mods.Cnc/OpenRA.Mods.Cnc.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>netstandard2.1</TargetFramework>
+    <TargetFramework Condition="'$(Mono)' == ''">net5.0</TargetFramework>
+    <TargetFramework Condition="'$(Mono)' != ''">netstandard2.1</TargetFramework>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Optimize>true</Optimize>
     <LangVersion>7.3</LangVersion>
diff --git a/OpenRA.Mods.Common/OpenRA.Mods.Common.csproj b/OpenRA.Mods.Common/OpenRA.Mods.Common.csproj
index cf243e0eb1..12290c97b6 100644
--- a/OpenRA.Mods.Common/OpenRA.Mods.Common.csproj
+++ b/OpenRA.Mods.Common/OpenRA.Mods.Common.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>netstandard2.1</TargetFramework>
+    <TargetFramework Condition="'$(Mono)' == ''">net5.0</TargetFramework>
+    <TargetFramework Condition="'$(Mono)' != ''">netstandard2.1</TargetFramework>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Optimize>true</Optimize>
     <LangVersion>7.3</LangVersion>
diff --git a/OpenRA.Mods.Common/Traits/BotModules/BotModuleLogic/BaseBuilderQueueManager.cs b/OpenRA.Mods.Common/Traits/BotModules/BotModuleLogic/BaseBuilderQueueManager.cs
index f646e58d90..c6fbb4af8b 100644
--- a/OpenRA.Mods.Common/Traits/BotModules/BotModuleLogic/BaseBuilderQueueManager.cs
+++ b/OpenRA.Mods.Common/Traits/BotModules/BotModuleLogic/BaseBuilderQueueManager.cs
@@ -147,7 +147,7 @@ namespace OpenRA.Mods.Common.Traits
 					var possibleBuilding = world.ActorsWithTrait<Pluggable>().FirstOrDefault(a =>
 						a.Actor.Owner == player && a.Trait.AcceptsPlug(a.Actor, plugInfo.Type));
 
-					if (possibleBuilding != null)
+					if (possibleBuilding.Actor != null)
 					{
 						orderString = "PlacePlug";
 						location = possibleBuilding.Actor.Location + possibleBuilding.Trait.Info.Offset;
diff --git a/OpenRA.Mods.D2k/OpenRA.Mods.D2k.csproj b/OpenRA.Mods.D2k/OpenRA.Mods.D2k.csproj
index f8af8a5026..75923b2b76 100644
--- a/OpenRA.Mods.D2k/OpenRA.Mods.D2k.csproj
+++ b/OpenRA.Mods.D2k/OpenRA.Mods.D2k.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>netstandard2.1</TargetFramework>
+    <TargetFramework Condition="'$(Mono)' == ''">net5.0</TargetFramework>
+    <TargetFramework Condition="'$(Mono)' != ''">netstandard2.1</TargetFramework>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Optimize>true</Optimize>
     <LangVersion>7.3</LangVersion>
diff --git a/OpenRA.Platforms.Default/OpenRA.Platforms.Default.csproj b/OpenRA.Platforms.Default/OpenRA.Platforms.Default.csproj
index e633a24c46..e881950c3a 100644
--- a/OpenRA.Platforms.Default/OpenRA.Platforms.Default.csproj
+++ b/OpenRA.Platforms.Default/OpenRA.Platforms.Default.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-      <TargetFramework>netstandard2.1</TargetFramework>
+    <TargetFramework Condition="'$(Mono)' == ''">net5.0</TargetFramework>
+    <TargetFramework Condition="'$(Mono)' != ''">netstandard2.1</TargetFramework>
       <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
       <Optimize>true</Optimize>
       <LangVersion>7.3</LangVersion>