diff --git a/sys/src/cmd/deroff.c b/sys/src/cmd/deroff.c
index 914c5a3f5..ce0cee95b 100644
--- a/sys/src/cmd/deroff.c
+++ b/sys/src/cmd/deroff.c
@@ -745,7 +745,7 @@ eqn(void)
 		}
 		if(c != '\n')
 			while(C1 != '\n') { 
-				if(chars[c] == PUNCT)
+				if(charclass(c) == PUNCT)
 					last = c;
 				else
 				if(c != ' ')