diff --git a/backoff/_wait_gen.py b/backoff/_wait_gen.py
index 33b37b8..1b54dde 100644
--- a/backoff/_wait_gen.py
+++ b/backoff/_wait_gen.py
@@ -22,12 +22,12 @@ def expo(
     """
     # Advance past initial .send() call
     yield  # type: ignore[misc]
-    n = 0
+    base_n: float = 1
     while True:
-        a = factor * base ** n
+        a = factor * base_n
         if max_value is None or a < max_value:
             yield a
-            n += 1
+            base_n *= base
         else:
             yield max_value
 
diff --git a/tests/test_wait_gen.py b/tests/test_wait_gen.py
index a658712..bebe58b 100644
--- a/tests/test_wait_gen.py
+++ b/tests/test_wait_gen.py
@@ -67,6 +67,14 @@ def test_expo_max_value():
         assert expect == next(gen)
 
 
+def test_expo_max_value_factor():
+    gen = backoff.expo(factor=3, max_value=2 ** 4)
+    gen.send(None)
+    expected = [3 * 1, 3 * 2, 3 * 4, 16, 16, 16, 16]
+    for expect in expected:
+        assert expect == next(gen)
+
+
 def test_fibo():
     gen = backoff.fibo()
     gen.send(None)