diff --git a/Makefile b/Makefile
index c64f2d5eac..b6a77509e6 100644
--- a/Makefile
+++ b/Makefile
@@ -72,7 +72,7 @@ OPENRA_UTILITY = ENGINE_DIR=".." $(MONO) --debug bin/OpenRA.Utility.dll
 #
 all:
 	@command -v $(firstword $(MSBUILD)) >/dev/null || (echo "OpenRA requires the '$(MSBUILD)' tool provided by Mono >= 5.18."; exit 1)
-	@$(MSBUILD) -t:Build -restore -p:Configuration=Release -p:TargetPlatform=$(TARGETPLATFORM) -p:Mono=true -p:DefineConstants="MONO"
+	@$(MSBUILD) -t:Build -restore -p:Configuration=Release -p:TargetPlatform=$(TARGETPLATFORM) -p:Mono=true
 ifeq ($(TARGETPLATFORM), unix-generic)
 	@./configure-system-libraries.sh
 endif
@@ -86,7 +86,7 @@ clean:
 check:
 	@echo
 	@echo "Compiling in debug mode..."
-	@$(MSBUILD) -t:build -restore -p:Configuration=Debug -p:TargetPlatform=$(TARGETPLATFORM) -p:Mono=true -p:DefineConstants="MONO"
+	@$(MSBUILD) -t:build -restore -p:Configuration=Debug -p:TargetPlatform=$(TARGETPLATFORM) -p:Mono=true
 	@echo
 	@echo "Checking for explicit interface violations..."
 	@$(OPENRA_UTILITY) all --check-explicit-interfaces
diff --git a/OpenRA.Game/OpenRA.Game.csproj b/OpenRA.Game/OpenRA.Game.csproj
index a5cb108d95..9429db8c10 100644
--- a/OpenRA.Game/OpenRA.Game.csproj
+++ b/OpenRA.Game/OpenRA.Game.csproj
@@ -31,6 +31,9 @@
     <DefineConstants>DEBUG;TRACE</DefineConstants>
     <Optimize>false</Optimize>
   </PropertyGroup>
+  <PropertyGroup Condition="'$(Mono)' != ''">
+    <DefineConstants>MONO</DefineConstants>
+  </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="OpenRA-Eluant" Version="1.0.17" />
     <PackageReference Include="OpenRA-Open.NAT" Version="1.0.0" />
diff --git a/packaging/functions.sh b/packaging/functions.sh
index ea9aacdd24..37d5260ab8 100755
--- a/packaging/functions.sh
+++ b/packaging/functions.sh
@@ -34,7 +34,7 @@ install_assemblies_mono() {
 	rm -rf "${SRC_PATH}/OpenRA."*/obj
 	rm -rf "${SRC_PATH:?}/bin"
 
-	msbuild -verbosity:m -nologo -t:Build -restore -p:Configuration=Release -p:TargetPlatform="${TARGETPLATFORM}" -p:Mono=true -p:DefineConstants="MONO"
+	msbuild -verbosity:m -nologo -t:Build -restore -p:Configuration=Release -p:TargetPlatform="${TARGETPLATFORM}" -p:Mono=true
 	if [ "${TARGETPLATFORM}" = "unix-generic" ]; then
 		./configure-system-libraries.sh
 	fi