diff --git a/src/openrct2-ui/drawing/engines/opengl/DrawRectShader.h b/src/openrct2-ui/drawing/engines/opengl/DrawRectShader.h
index 01cfb9d3d6..b1cbb415d1 100644
--- a/src/openrct2-ui/drawing/engines/opengl/DrawRectShader.h
+++ b/src/openrct2-ui/drawing/engines/opengl/DrawRectShader.h
@@ -50,7 +50,7 @@ private:
     GLuint _vboInstances;
     GLuint _vao;
 
-    GLsizei _instanceCount;
+    GLsizei _instanceCount = 0;
 
 public:
     DrawRectShader();