diff --git a/nilmdb/server/nilmdb.py b/nilmdb/server/nilmdb.py
index 8f1949f..9b1407e 100644
--- a/nilmdb/server/nilmdb.py
+++ b/nilmdb/server/nilmdb.py
@@ -142,11 +142,13 @@ class NilmDB(object):
             with self.con:
                 cur.execute("PRAGMA user_version = {v:d}".format(v=version))
 
-    def _fill_in_limits(self, start, end):
+    def _check_user_times(self, start, end):
         if start is None:
             start = -1e12
         if end is None:
             end = 1e12
+        if start >= end:
+            raise NilmDBError("start must precede end")
         return (start, end)
 
     @nilmdb.utils.lru_cache(size = 16)
@@ -310,7 +312,7 @@ class NilmDB(object):
         """
         stream_id = self._stream_id(path)
         intervals = self._get_intervals(stream_id)
-        (start, end) = self._fill_in_limits(start, end)
+        (start, end) = self._check_user_times(start, end)
         requested = Interval(start, end)
         result = []
         for n, i in enumerate(intervals.intersection(requested)):
@@ -483,7 +485,7 @@ class NilmDB(object):
         stream_id = self._stream_id(path)
         table = self.data.getnode(path)
         intervals = self._get_intervals(stream_id)
-        (start, end) = self._fill_in_limits(start, end)
+        (start, end) = self._check_user_times(start, end)
         requested = Interval(start, end)
         result = []
         matched = 0
@@ -530,7 +532,7 @@ class NilmDB(object):
         stream_id = self._stream_id(path)
         table = self.data.getnode(path)
         intervals = self._get_intervals(stream_id)
-        (start, end) = self._fill_in_limits(start, end)
+        (start, end) = self._check_user_times(start, end)
         to_remove = Interval(start, end)
         removed = 0