diff --git a/Pipfile b/Pipfile
index 14851a96..2c684401 100644
--- a/Pipfile
+++ b/Pipfile
@@ -25,3 +25,4 @@ uritemplate = "*"
 coveralls = "*"
 flake8 = "*"
 ipaddress = "*"
+tblib = "*"
diff --git a/reports/graphs/sleep_pattern.py b/reports/graphs/sleep_pattern.py
index e7e67295..98c6671c 100644
--- a/reports/graphs/sleep_pattern.py
+++ b/reports/graphs/sleep_pattern.py
@@ -83,9 +83,11 @@ def sleep_pattern(instances):
         if start_time.utcoffset() != end_time.utcoffset():
             diff = start_time.utcoffset() - end_time.utcoffset()
             duration -= timezone.timedelta(seconds=diff.seconds)
-            times[len(times) - 1] = duration.seconds/60
-            labels[len(labels) - 1] = _format_label(duration, start_time,
-                                                    end_time)
+            yesterday = (end_time - timezone.timedelta(days=1))
+            yesterday = yesterday.date().isoformat()
+            times[yesterday][len(times[yesterday]) - 1] = duration.seconds/60
+            labels[yesterday][len(times[yesterday]) - 1] = _format_label(
+                duration, start_time, end_time)
 
         last_end_time = end_time