diff --git a/gain_viz/app.py b/gain_viz/app.py
index 13b7ca3..3272b21 100644
--- a/gain_viz/app.py
+++ b/gain_viz/app.py
@@ -252,7 +252,7 @@ def save_config():
         'center_freq': center_freq,
         'sample_rate': sample_rate,
         'fft_size': NFFT,
-        'window_ms': window_ms
+        'window_ms': window_ms,
         'tcp_port' : tcp_port
     }
     with open('/opt/gain-viz/config.json', 'w') as f: