diff --git a/examples/demo/fibonacci_memo.js b/examples/demo/fibonacci_memo.js
index 9dbd1f4..300a514 100644
--- a/examples/demo/fibonacci_memo.js
+++ b/examples/demo/fibonacci_memo.js
@@ -10,4 +10,4 @@ const result = fibonacci(621);
 const end = performance.now();
 
 console.log(`fibonacci(621) = ${result}`);
-console.log(`Time: ${(end - start).toFixed(2)} ms`);
+console.log(`Time: ${(end - start).toFixed(4)} ms (${((end - start) * 1000).toFixed(2)} µs)`);
diff --git a/examples/demo/fibonacci_tco.js b/examples/demo/fibonacci_tco.js
index e8d77e3..d99c523 100644
--- a/examples/demo/fibonacci_tco.js
+++ b/examples/demo/fibonacci_tco.js
@@ -8,4 +8,4 @@ const result = fib(30);
 const end = performance.now();
 
 console.log(`fibonacci(30) = ${result}`);
-console.log(`Time: ${(end - start).toFixed(2)} ms`);
+console.log(`Time: ${(end - start).toFixed(4)} ms (${((end - start) * 1000).toFixed(2)} µs)`);
diff --git a/src/ant.c b/src/ant.c
index bfb1251..dc6937e 100644
--- a/src/ant.c
+++ b/src/ant.c
@@ -7222,6 +7222,7 @@ jsval_t call_js_internal(
     tc_args = js->tc.args;
     js->tc.args = NULL;
     tc_argc = js->tc.argc;
+    tc_iter = true;
     continue;
   }
 
diff --git a/tests/test_tco_zeroarg.js b/tests/test_tco_zeroarg.js
new file mode 100644
index 0000000..026e6b5
--- /dev/null
+++ b/tests/test_tco_zeroarg.js
@@ -0,0 +1,23 @@
+// Test: verify zero-arg tail call actually uses TCO by going deep enough to
+// guarantee a stack overflow without it.
+
+// Pure zero-arg self-recursion with no parameters at all
+let n = 0;
+function go() {
+  n++;
+  if (n >= 1000000) return 'ok';
+  return go();
+}
+const r = go();
+console.log('result:', r, 'n:', n);
+if (r !== 'ok') { console.log('FAIL'); process.exit(1); }
+
+// Zero-arg mutual recursion
+let m = 0;
+function a() { m++; if (m >= 1000000) return m; return b(); }
+function b() { m++; if (m >= 1000000) return m; return a(); }
+const r2 = a();
+console.log('mutual result:', r2);
+if (r2 !== 1000000) { console.log('FAIL'); process.exit(1); }
+
+console.log('PASS');