diff --git a/src/app/App.tsx b/src/app/App.tsx
index bd5da429..a609dbde 100644
--- a/src/app/App.tsx
+++ b/src/app/App.tsx
@@ -168,6 +168,16 @@ function readYawDegreesDraft(source: string): number {
   return normalizeYawDegrees(yawDegrees);
 }
 
+function readNonNegativeNumberDraft(source: string, label: string): number {
+  const value = Number(source);
+
+  if (!Number.isFinite(value) || value < 0) {
+    throw new Error(`${label} must be a finite number greater than or equal to zero.`);
+  }
+
+  return value;
+}
+
 function areVec2Equal(left: Vec2, right: Vec2): boolean {
   return left.x === right.x && left.y === right.y;
 }