diff --git a/shared/static/scripts/sx.js b/shared/static/scripts/sx.js
index c655a2e..3d0c094 100644
--- a/shared/static/scripts/sx.js
+++ b/shared/static/scripts/sx.js
@@ -650,6 +650,9 @@
       if (name === "true") return true;
       if (name === "false") return false;
       if (name === "nil") return NIL;
+      // Debug: log env keys to help diagnose
+      var envKeys = Object.keys(env).filter(function(k) { return typeof env[k] !== "function"; }).slice(0, 20);
+      console.error("Undefined symbol: " + name + " | env keys (non-fn): " + envKeys.join(", "));
       throw new Error("Undefined symbol: " + name);
     }