diff --git a/pypulse/singlepulse.py b/pypulse/singlepulse.py
index 7faa37a..29b8b30 100644
--- a/pypulse/singlepulse.py
+++ b/pypulse/singlepulse.py
@@ -735,6 +735,9 @@ def getTbin(self):
         """ Return the time unit of one phase bin """
         if self.getPeriod() is not None:
             return self.getPeriod()/self.getNbins()
+        else:
+            raise ValueError("Cannot get bin time; period is not set")
+
 
     def plot(self, show=True):
         """