diff --git a/src/MC/fix_gcmc.h b/src/MC/fix_gcmc.h
index 88d05e022c..3001a533d7 100644
--- a/src/MC/fix_gcmc.h
+++ b/src/MC/fix_gcmc.h
@@ -272,4 +272,8 @@ E: Too many total atoms
 
 See the setting for bigint in the src/lmptype.h file.
 
+E: Fix gcmc put atom outside box
+
+An attempt was made to move an atom outside the box boundaries
+
 */