diff --git a/sys/src/cmd/cc/dpchk.c b/sys/src/cmd/cc/dpchk.c
index aa7d468b8..217e005c3 100644
--- a/sys/src/cmd/cc/dpchk.c
+++ b/sys/src/cmd/cc/dpchk.c
@@ -76,9 +76,9 @@ getflag(char *s)
 	nstar = 0;
 	while(fmt < e){
 		s += chartorune(&c, s);
-		fmt += runetochar(fmt, &c);
 		if(c == 0 || c >= nelem(flagbits))
 			break;
+		fmt += runetochar(fmt, &c);
 		f = flagbits[c];
 		switch(f) {
 		case Fnone: