diff --git a/Source/Plugins/BuilderModes/BuilderModesMono.csproj b/Source/Plugins/BuilderModes/BuilderModesMono.csproj
index 9cfd1a84..2f355b53 100644
--- a/Source/Plugins/BuilderModes/BuilderModesMono.csproj
+++ b/Source/Plugins/BuilderModes/BuilderModesMono.csproj
@@ -503,6 +503,7 @@
     <Compile Include="VisualModes\EffectPlaneCopySlope.cs" />
     <Compile Include="VisualModes\EffectThingLineSlope.cs" />
     <Compile Include="VisualModes\EffectThingSlope.cs" />
+    <Compile Include="VisualModes\EffectSRB2ThingVertexSlope.cs" />
     <Compile Include="VisualModes\EffectThingVertexSlope.cs" />
     <Compile Include="VisualModes\EffectTransferCeilingBrightness.cs" />
     <Compile Include="VisualModes\EffectTransferFloorBrightness.cs" />