diff --git a/km3buu/output.py b/km3buu/output.py
index 7dd519f39a6280eec4730dd3c4507e759c46b5c5..c5cdd3c3a0da21f7e591d61cca59e763eeb2300a 100644
--- a/km3buu/output.py
+++ b/km3buu/output.py
@@ -353,7 +353,7 @@ class GiBUUOutput:
                                    bounds_error=False)
             return lambda e: xsec_interp(e) * e
 
-    def global_generation_weight(solid_angle):
+    def global_generation_weight(self, solid_angle):
         # I_E * I_theta * t_gen (* #NuTypes)
         if self.flux_data is not None:
             energy_phase_space = self.flux_interpolation.integral(