diff --git a/usr.bin/grep/regex/tre-fastmatch.c b/usr.bin/grep/regex/tre-fastmatch.c
index 6f1aec6bf3b7..b7a7c91fbcfd 100644
--- a/usr.bin/grep/regex/tre-fastmatch.c
+++ b/usr.bin/grep/regex/tre-fastmatch.c
@@ -468,7 +468,7 @@ static int	fastcmp(const fastmatch_t *fg, const void *data,
   fg->nosub = (cflags & REG_NOSUB);					\
 									\
   /* Cannot handle REG_ICASE with MB string */				\
-  if (fg->icase && (TRE_MB_CUR_MAX > 1))				\
+  if (fg->icase && (TRE_MB_CUR_MAX > 1) && n > 0)			\
     {									\
       DPRINT(("Cannot use fast matcher for MBS with REG_ICASE\n"));	\
       return REG_BADPAT;						\