diff --git a/usr.sbin/pw/pw_user.c b/usr.sbin/pw/pw_user.c
index 76849ba95546..a71be12def40 100644
--- a/usr.sbin/pw/pw_user.c
+++ b/usr.sbin/pw/pw_user.c
@@ -1087,10 +1087,10 @@ split_groups(StringList **groups, char *groupsstr)
 	char *p;
 	char tok[] = ", \t";
 
+	if (*groups == NULL)
+		*groups = sl_init();
 	for (p = strtok(groupsstr, tok); p != NULL; p = strtok(NULL, tok)) {
 		grp = group_from_name_or_id(p);
-		if (*groups == NULL)
-			*groups = sl_init();
 		sl_add(*groups, newstr(grp->gr_name));
 	}
 }
diff --git a/usr.sbin/pw/tests/pw_usermod_test.sh b/usr.sbin/pw/tests/pw_usermod_test.sh
index 6a1313025cd2..cf3622f3b222 100755
--- a/usr.sbin/pw/tests/pw_usermod_test.sh
+++ b/usr.sbin/pw/tests/pw_usermod_test.sh
@@ -128,6 +128,9 @@ user_mod_nogroups_body() {
 	atf_check -s exit:0 ${PW} usermod foo -G test3,test4
 	atf_check -s exit:0 -o inline:"test3\ntest4\n" \
 		awk -F\: '$4 == "foo" { print $1 }' ${HOME}/group
+	atf_check -s exit:0 ${PW} usermod foo -G ""
+	atf_check -s exit:0 -o empty \
+		awk -F\: '$4 == "foo" { print $1 }' ${HOME}/group
 }
 
 atf_test_case user_mod_rename