diff --git a/src/error.rs b/src/error.rs
index 0de51f9..5bc30a6 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -40,3 +40,5 @@ impl Display for RenderError {
         }
     }
 }
+
+impl Error for RenderError {}
diff --git a/src/shader.wgsl b/src/shader.wgsl
index b60c8b6..53f78ce 100644
--- a/src/shader.wgsl
+++ b/src/shader.wgsl
@@ -12,7 +12,7 @@ struct VertexOutput {
     @invariant @builtin(position) position: vec4<f32>,
     @location(0) color: vec4<f32>,
     @location(1) uv: vec2<f32>,
-    @location(2) content_type: u32,
+    @location(2) @interpolate(flat) content_type: u32,
 };
 
 struct Params {