diff --git a/doc/src/fix_gcmc.txt b/doc/src/fix_gcmc.txt
index 41ec38cffb18c674575a884543fcaa3eb04b705c..405738276f8f5a194907e4df2d5c9e4a8e78cb63 100644
--- a/doc/src/fix_gcmc.txt
+++ b/doc/src/fix_gcmc.txt
@@ -383,6 +383,9 @@ called.  Reneighboring is required.
 Can be run in parallel, but aspects of the GCMC part will not scale
 well in parallel. Only usable for 3D simulations.
 
+When using fix gcmc in combination with fix shake or fix rigid,
+only gcmc exchange moves are supported.
+
 Note that very lengthy simulations involving insertions/deletions of
 billions of gas molecules may run out of atom or molecule IDs and
 trigger an error, so it is better to run multiple shorter-duration