clang3.9.1 util.c - comparison of unsigned expression < 0 is always false

[gtirloni]

Environment

Fedora 26 x86_64
clang 3.9.1
git faef420

Error

/usr/bin/clang -DHAVE_CONFIG_H -I. -I..    -Wall -Werror -DVERSIONCOMMIT=\""0.8.1, commit: `git describe --dirty --always --tags 2> /dev/null || true`"\" -g -O2 -MT util.o -MD -MP -MF $depbase.Tpo -c -o util.o util.c &&\
mv -f $depbase.Tpo $depbase.Po
util.c:251:9: error: comparison of unsigned expression < 0 is always false [-Werror,-Wtautological-compare]
                if (l < 0) {
                    ~ ^ ~
1 error generated.
make[2]: *** [Makefile:362: util.o] Error 1