%if ! %{with clang}
# On x86_64 architectures, Mozilla can build up to 4 jobs at once in parallel,
# however builds tend to fail on other arches when building in parallel.
-RPM_BUILD_NR_THREADS=$(echo %{_smp_mflags} | cut -dj -f2)
-%ifarch %{x8864}
-[ -n "RPM_BUILD_NR_THREADS" -a "$RPM_BUILD_NR_THREADS" -gt 4 ] && RPM_BUILD_NR_THREADS=4
-%else
RPM_BUILD_NR_THREADS=1
+%ifarch %{x8664}
+jobs=$(echo %{_smp_mflags} | cut -dj -f2)
+[ -n "$jobs" -a "$jobs" -gt 4 ] && RPM_BUILD_NR_THREADS=4 || RPM_BUILD_NR_THREADS="$jobs"
%endif
export MOZ_MAKE_FLAGS="-j${RPM_BUILD_NR_THREADS}"
%endif