diff --git a/src/interpreter.mjs b/src/interpreter.mjs
index fb5bcdd..2d1a651 100644
--- a/src/interpreter.mjs
+++ b/src/interpreter.mjs
@@ -12,7 +12,7 @@
 // flag is truthy, bounded by ctx.maxIterations. Commands run top-to-bottom.
 
 export function tokenize(src) {
-  const re = /("(?:[^"\\]|\\.)*")|(\/\/[^\n]*)|(\d+(?:\.\d+)?)|([A-Za-z_]\w*)|([(){};,])|(\s+)/g;
+  const re = /("(?:[^"\\]|\\.)*")|(\/\/[^\n]*)|(-?\d+(?:\.\d+)?)|([A-Za-z_]\w*)|([(){};,])|(\s+)/g;
   const tokens = [];
   let m;
   let lastIndex = 0;
diff --git a/test/interpreter.test.mjs b/test/interpreter.test.mjs
index 41f71d0..a1322d7 100644
--- a/test/interpreter.test.mjs
+++ b/test/interpreter.test.mjs
@@ -1,6 +1,7 @@
 import assert from "node:assert/strict";
 import test from "node:test";
-import { compile, tokenize } from "../src/interpreter.mjs";
+import { defaultCommands } from "../src/commands.mjs";
+import { compile, run, tokenize } from "../src/interpreter.mjs";
 
 test("tokenize rejects unexpected characters between valid tokens", () => {
   assert.throws(() => tokenize("say(@);"), /unexpected character/);
@@ -15,6 +16,18 @@ test("compile preserves valid moshscript behavior", () => {
   });
 });
 
+test("negative numeric arguments reach command validation", async () => {
+  const ast = compile("sleep(-1);");
+  const ctx = {
+    vars: { alive: true },
+    iter: 0,
+    maxIterations: 1,
+    commands: defaultCommands(),
+  };
+
+  await assert.rejects(() => run(ast, ctx), /finite non-negative number/);
+});
+
 test("compile requires commas between call arguments", () => {
   assert.throws(() => compile("say(\"one\" \"two\");"), /expected comma/);
   assert.throws(() => compile("say(\"one\",);"), /expected argument after comma/);