diff --git a/calc.js b/calc.js
index 3265688..24b893c 100644
--- a/calc.js
+++ b/calc.js
@@ -268,6 +268,11 @@ function parseAndCalculate(line) {
     }
   }
 
+  // Pre-checking before the calculator throws unreadable errors.
+  if (!gen.species.get(attacker)) throw Error(`No species ${attacker}`);
+  if (!gen.species.get(defender)) throw Error(`No species ${attacker}`);
+  if (!gen.moves.get(move)) throw Error(`No move ${move}`);
+
   return calculate(
     gen,
     new Pokemon(gen, attacker, attackerOpts),