diff --git a/doc/source/reference_manual/ctobssim.rst b/doc/source/reference_manual/ctobssim.rst
index 4625936..f6caca0 100644
--- a/doc/source/reference_manual/ctobssim.rst
+++ b/doc/source/reference_manual/ctobssim.rst
@@ -23,7 +23,7 @@ subsequent runs will lead to different event samples.
 
 ctobssim performs a safety check on the maximum photon rate for all model 
 components to avoid that the tool locks up and requests huge memory 
-ressources, which may happen if a mistake was made in setting up the input 
+resources, which may happen if a mistake was made in setting up the input 
 model (for example if an error in the flux units is made). The maximum allowed
 photon rate is controlled by the hidden ``maxrate`` parameter, which by default 
 is set to 1e6.