diff --git a/tools/push3-transpiler/src/transpiler.ts b/tools/push3-transpiler/src/transpiler.ts
index 4f13c17..9924769 100644
--- a/tools/push3-transpiler/src/transpiler.ts
+++ b/tools/push3-transpiler/src/transpiler.ts
@@ -391,10 +391,15 @@ export function transpile(program: Node): TranspileResult {
   processItems(program.items, state);
 
   // Pop 4 outputs: top → ci, then anchorShare, anchorWidth, discoveryDepth.
-  const ciVar             = state.dStack.pop() ?? '0';
-  const anchorShareVar    = state.dStack.pop() ?? '0';
-  const anchorWidthVar    = state.dStack.pop() ?? '0';
-  const discoveryDepthVar = state.dStack.pop() ?? '0';
+  if (state.dStack.length < 4) {
+    throw new Error(
+      `Program must leave exactly 4 values on the DYADIC stack; found ${state.dStack.length}`,
+    );
+  }
+  const ciVar             = state.dStack.pop()!;
+  const anchorShareVar    = state.dStack.pop()!;
+  const anchorWidthVar    = state.dStack.pop()!;
+  const discoveryDepthVar = state.dStack.pop()!;
 
   return { functionBody: state.lines, ciVar, anchorShareVar, anchorWidthVar, discoveryDepthVar };
 }