diff --git a/src/SHOCK/fix_append_atoms.h b/src/SHOCK/fix_append_atoms.h
index 1368d164b62a3b24cd9838d4738e96c8dc3f7e80..d9885998bea9f68fa3894b36d7c2d7d1643436f6 100644
--- a/src/SHOCK/fix_append_atoms.h
+++ b/src/SHOCK/fix_append_atoms.h
@@ -79,8 +79,7 @@ must be of type m (shrink/minimum).
 
 E: Bad fix ID in fix append/atoms command
 
-The value of the fix_id for keyword spatial must start with the suffix
-f_.
+The value of the fix_id for keyword spatial must start with 'f_'.
 
 E: Invalid basis setting in fix append/atoms command