diff --git a/src/+gui_auxiliary/set_command_option.m b/src/+gui_auxiliary/set_command_option.m
index 2a71003bd82ddf34d2140b82ec5ef2c714a7a609..8cc0daca6e02dc98d2fa0d94163853c25dad50ff 100644
--- a/src/+gui_auxiliary/set_command_option.m
+++ b/src/+gui_auxiliary/set_command_option.m
@@ -73,7 +73,7 @@ try
             end
 
         case 'first_obs'
-            options_.first_obs = value;
+            options_.first_obs = str2num(value);
 
         case 'use_bandpass_filter'
             options_.bandpass.indicator = value;