diff --git a/pvlib/singlediode.py b/pvlib/singlediode.py
index cb5b8e6b13..d0ad27e995 100644
--- a/pvlib/singlediode.py
+++ b/pvlib/singlediode.py
@@ -13,7 +13,8 @@
 try:
     from scipy.optimize import brentq
 except ImportError:
-    brentq = NotImplemented
+    def brentq(): raise NotImplementedError(
+        "brentq can't be imported because scipy isn't installed")
 
 # FIXME: change this to newton when scipy-1.2 is released
 try: