source-highlight hangs when using zsh.lang languge definition

When the source-highlight language definition is set to zsh.lang, the program hangs. It doesn't hang when set to other language definitions.

To reproduce:

source-highlight --failsafe -f esc --lang-def=zsh.lang --style-file=esc.style -i /path/to/zsh/script

What happens:

Nothing. I have to use CTRL-C to quit.

What I expected:

Syntax highlighted output

Other information:

If I use a different language definition, I get the highlighted output almost immediately. For example, the following command works without a problem:

source-highlight --failsafe -f esc --lang-def=sh.lang --style-file=esc.style -i /path/to/zsh/script

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: source-highlight 3.1.8-1.1
ProcVersionSignature: Ubuntu 4.4.0-21.37-generic 4.4.6
Uname: Linux 4.4.0-21-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
CurrentDesktop: XFCE
Date: Thu May 5 10:09:06 2016
SourcePackage: source-highlight
UpgradeStatus: Upgraded to xenial on 2016-05-04 (0 days ago)