diff --git a/src/planetsmath/functions.py b/src/planetsmath/functions.py
index 65142fd..60f2273 100644
--- a/src/planetsmath/functions.py
+++ b/src/planetsmath/functions.py
@@ -31,9 +31,9 @@ def sum_product(list):
 
 
 def multiply_by_2(list):
-    product = 1.0
+    product = 2.0
     for item in list:
-        product *= 2
+        item *= product
     return product