ipv4.ip_forward=0 not persisting in RHEL 7.3

I've entered the following in sysctl.conf:

net.ipv4.ip_forward=0

and yet upon reboot, if I run:

/sbin/sysctl -a | grep net.ipv4.ip_forward

I am always returned a 1, unless I manually enter:

sysctl -p /etc/sysctl.conf

...which obviously doesn't survive a reboot.

I've also checked for this entry in conf files at the following locations:

/usr/lib/sysctl.d
/run/sysctl.d
/etc/sysctl.d

...and even tried entering the same rule into the conf files at these locations, if they exist.

I'm not sure what else to do at this point. Am I missing something...? This is driving me nuts.