Error: Required module `Event' is unavailable

How can I solve this error? I get this when I try to do opam install ocaml-top

[ERROR] The compilation of ocaml-top failed at "ocp-build ocaml-top".

#=== ERROR while installing ocaml-top.1.1.3 ===================================#
# opam-version 1.2.2
# os           linux
# command      ocp-build ocaml-top
# path         /home/xyz/.opam/4.04.1/build/ocaml-top.1.1.3
# compiler     4.04.1
# exit-code    2
# env-file     /home/xyz/.opam/4.04.1/build/ocaml-top.1.1.3/ocaml-top-118181-6e1ea1.env
# stdout-file  /home/xyz/.opam/4.04.1/build/ocaml-top.1.1.3/ocaml-top-118181-6e1ea1.out
# stderr-file  /home/xyz/.opam/4.04.1/build/ocaml-top.1.1.3/ocaml-top-118181-6e1ea1.err
### stderr ###
# [...]
# 2 errors in 0.49s. 37 jobs (parallelism 3.1x), 47 files generated.
# Error log:
# Error:
# [57.1] '/home/xyz/.opam/4.04.1/bin/ocamlc.opt' '-thread' '-o' './_obuild/ocaml-top/ocaml-top.byte' './_obuild/ocaml-top/sigint_unix.o' '-I' './_obuild/ocaml-top' '-I' './src' '-I' '/home/xyz/.opam/4.04.1/lib/ocaml' '-I' '/home/xyz/.opam/4.04.1/lib/ocp-index/lib' '-I' '/home/xyz/.opam/4.04.1/lib/ocp-indent/lib' '-I' '/home/xyz/.opam/4.04.1/lib/ocp-indent/utils' '-I' '/home/xyz/.opam/4.04.1/lib/ocp-indent/lexer' '-I' '/home/xyz/.opam/4.04.1/lib/lablgtk2' '-I' '/home/xyz/.opam/4.04.1/lib/ocaml/compiler-libs' '/home/xyz/.opam/4.04.1/lib/ocaml/unix.cma' '/home/xyz/.opam/4.04.1/lib/ocaml/compiler-libs/ocamlcommon.cma' '/home/xyz/.opam/4.04.1/lib/lablgtk2/lablgtk.cma' '/home/xyz/.opam/4.04.1/lib/lablgtk2/lablgtksourceview2.cma' '/home/xyz/.opam/4.04.1/lib/ocp-indent/lexer/ocp-indent.lexer.cma' '/home/xyz/.opam/4.04.1/lib/ocp-indent/utils/ocp-indent.utils.cma' '/home/xyz/.opam/4.04.1/lib/ocp-indent/lib/ocp-indent.lib.cma' '/home/xyz/.opam/4.04.1/lib/ocp-index/lib/ocp-index-lib.cma' '/home/xyz/.opam/4.04.1/lib/ocaml/str.cma' '-custom' './_obuild/ocaml-top/tools.cmo' './_obuild/ocaml-top/cfg.cmo' './_obuild/ocaml-top/ocamlBuffer.cmo' './_obuild/ocaml-top/completion.cmo' './_obuild/ocaml-top/top.cmo' './_obuild/ocaml-top/topUi.cmo' './_obuild/ocaml-top/gui.cmo' './_obuild/ocaml-top/main.cmo'
# 
# File "_none_", line 1:
# Error: Required module `Event' is unavailable
# 
# Error:
# rule 57: target ./_obuild/ocaml-top/ocaml-top.byte not built

I'm also encountering this error. I'm using OS X High Sierra with Xcode 9 Beta.

A workaround would be to simply do:

opam install ocaml-top.1.1.2
opam pin add ocaml-top 1.1.2

The previous version of ocaml-top i.e. 1.1.2 does not suffer from this error during compilation.