diff --git a/scripts/graphstats.py b/scripts/graphstats.py
index 44c1a1fd3..f28685adc 100755
--- a/scripts/graphstats.py
+++ b/scripts/graphstats.py
@@ -51,6 +51,7 @@ def parse_log(logname, mcu):
     return out
 
 def setup_matplotlib(output_to_file):
+    global matplotlib
     if output_to_file:
         matplotlib.use('Agg')
     import matplotlib.pyplot, matplotlib.dates, matplotlib.font_manager