diff --git a/generate-html.py b/generate-html.py
index 9c06eca..95c4bbc 100755
--- a/generate-html.py
+++ b/generate-html.py
@@ -68,7 +68,7 @@ def load_overlay(overlay):
actual_pin = pinout.pins[pin]
if actual_pin['type'] in ['+3v3', '+5v', 'GND'] and overlay != 'ground':
- raise Exception("{} includes a reference to the {} pin, which isn't allowed".format(overlay, actual_pin['type']))
+ raise Exception("{} includes a reference to a {} pin, which isn't allowed".format(overlay, actual_pin['type']))
else:
uses += 1