diff --git a/SimPEG/Fields.py b/SimPEG/Fields.py
index f81cfb67..edd4cd92 100644
--- a/SimPEG/Fields.py
+++ b/SimPEG/Fields.py
@@ -71,13 +71,7 @@ class Fields(object):
         if type(srcTestList) is slice:
             ind = srcTestList
         else:
-            if type(srcTestList) is not list:
-                srcTestList = [srcTestList]
-            for srcTest in srcTestList:
-                if srcTest not in self.survey.srcList:
-                    raise KeyError('Invalid Source, not in survey list.')
-
-            ind = np.in1d(self.survey.srcList, srcTestList)
+            ind = self.survey.getSourceIndex(srcTestList)
         return ind
 
     def _nameIndex(self, name, accessType):
diff --git a/SimPEG/Survey.py b/SimPEG/Survey.py
index b6a17f28..0fdb0cd1 100644
--- a/SimPEG/Survey.py
+++ b/SimPEG/Survey.py
@@ -231,6 +231,11 @@ class BaseSurvey(object):
         [self._sourceOrder.setdefault(src.uid, ii) for ii, src in enumerate(self._srcList)]
 
     def getSourceIndex(self, sources):
+        if type(sources) is not list:
+            sources = [sources]
+        for src in sources:
+            if getattr(src,'uid',None) is None:
+                raise KeyError('Source does not have a uid: %s'%str(src))
         inds = map(lambda src: self._sourceOrder.get(src.uid, None), sources)
         if None in inds:
             raise KeyError('Some of the sources specified are not in this survey. %s'%str(inds))
diff --git a/SimPEG/Tests/test_SurveyAndData.py b/SimPEG/Tests/test_SurveyAndData.py
index 6feccc71..f02f14e8 100644
--- a/SimPEG/Tests/test_SurveyAndData.py
+++ b/SimPEG/Tests/test_SurveyAndData.py
@@ -49,7 +49,5 @@ class TestData(unittest.TestCase):
         self.assertRaises(KeyError, survey.getSourceIndex, [SrcNotThere])
         self.assertRaises(KeyError, survey.getSourceIndex, [srcs[1],srcs[2],SrcNotThere])
 
-
-
 if __name__ == '__main__':
     unittest.main()