diff --git a/bitbake/lib/bb/data_smart.py b/bitbake/lib/bb/data_smart.py
index 27fb7d9..2c02cde 100644
--- a/bitbake/lib/bb/data_smart.py
+++ b/bitbake/lib/bb/data_smart.py
@@ -102,7 +102,10 @@ class ExpansionError(Exception):
         self.expression = expression
         self.variablename = varname
         self.exception = exception
-        self.msg = "Failure expanding variable %s, expression was %s which triggered exception %s: %s" % (varname, expression, type(exception).__name__, exception)
+        if varname:
+            self.msg = "Failure expanding variable %s, expression was %s which triggered exception %s: %s" % (varname, expression, type(exception).__name__, exception)
+        else:
+            self.msg = "Failure expanding expression %s which triggered exception %s: %s" % (expression, type(exception).__name__, exception)
         Exception.__init__(self, self.msg)
         self.args = (varname, expression, exception)
     def __str__(self):