diff --git a/fib.py b/fib.py
index 421cfab..8631b73 100644
--- a/fib.py
+++ b/fib.py
@@ -8,7 +8,12 @@
 def fibonacci(position):
   if(position == 1 or position == 2):
     return 1
-  return fibonacci(position - 1) + fibonacci(position - 2)
+  elif (position == 0):
+    return 0
+  elif (position < 0):
+    return None 
+  else:
+    return fibonacci(position - 1) + fibonacci(position - 2)