diff --git a/src/engine/satellites.ts b/src/engine/satellites.ts
index 6427c2b..ff8ac9f 100644
--- a/src/engine/satellites.ts
+++ b/src/engine/satellites.ts
@@ -533,6 +533,18 @@ export function createSatelliteLayer(boardRadius: number): SatelliteLayer {
       uPixelRatio: { value: 1 },
     },
     vertexShader: `
+/*
+ * DECLARED HERE, and it has to be.
+ *
+ * ShaderMaterial prepends three own built-ins — projectionMatrix,
+ * modelViewMatrix, position and the rest — but it does NOT prepend the custom
+ * uniforms declared in the uniforms object above. Putting one there and using it
+ * in the body without declaring it here compiles nowhere: the program fails with
+ * "uPixelRatio : undeclared identifier", three logs a shader error, and this
+ * layer silently draws nothing while every other layer carries on. That shipped
+ * once, and the console error was the only symptom.
+ */
+uniform float uPixelRatio;
 attribute vec4 color;
 attribute float aSize;
 varying vec4 vColor;