diff --git a/doc/src/fix_gcmc.txt b/doc/src/fix_gcmc.txt
index 27c8c0aca6122871a85048231ae4c551c417fe37..f5ebe123f808f8c70203e77b06ef355fff6e1733 100644
--- a/doc/src/fix_gcmc.txt
+++ b/doc/src/fix_gcmc.txt
@@ -331,6 +331,10 @@ may no longer exist since it might have been deleted by the first
 fix gcmc command. An existing template molecule will need to be
 referenced by the user for each subsequent fix gcmc command.
 
+Because molecule insertion does not work in combination with
+fix rigid, simulataneous use of fix rigid or fix rigid/small 
+with this fix is not allowed.
+
 [Related commands:]
 
 "fix atom/swap"_fix_atom_swap.html,