diff --git a/ocaml-lablgtk.spec b/ocaml-lablgtk.spec
index e45c3b3..8685721 100644
--- a/ocaml-lablgtk.spec
+++ b/ocaml-lablgtk.spec
@@ -1,6 +1,8 @@
+%global opt %(test -x %{_bindir}/ocamlopt && echo 1 || echo 0)
+
 Name:           ocaml-lablgtk
 Version:        2.18.3
-Release:        5%{?dist}
+Release:        6%{?dist}
 
 Summary:        Objective Caml interface to gtk+
 
@@ -9,7 +11,6 @@ License:        LGPLv2 with exceptions
 URL:            http://lablgtk.forge.ocamlcore.org/
 Source:         https://forge.ocamlcore.org/frs/download.php/1479/lablgtk-%{version}.tar.gz
 
-ExcludeArch:    sparc64 s390 s390x
 
 Obsoletes:      lablgtk <= 2.6.0-7
 Provides:       lablgtk = 2.6.0-7
@@ -72,8 +73,12 @@ developing applications that use %{name}.
 unset MAKEFLAGS
 %configure --with-gl --enable-debug
 perl -pi -e "s|-O|$RPM_OPT_FLAGS|" src/Makefile
+%if %{opt}
 make world CAMLOPT="ocamlopt.opt -g"
 make opt CAMLOPT="ocamlopt.opt -g"
+%else
+make world CAMLC="ocamlc -g"
+%endif
 make doc CAMLP4O="camlp4o -I %{_libdir}/ocaml/camlp4/Camlp4Parsers"
 
 
@@ -114,7 +119,9 @@ find examples -name .cvsignore -exec rm {} \;
 %dir %{_libdir}/ocaml/lablgtk2
 %{_libdir}/ocaml/lablgtk2/*.cmi
 %{_libdir}/ocaml/lablgtk2/*.cma
+%if %{opt}
 %{_libdir}/ocaml/lablgtk2/*.cmxs
+%endif
 %{_libdir}/ocaml/stublibs/*.so*
 %{_bindir}/gdk_pixbuf_mlsource
 %{_bindir}/lablgladecc2
@@ -126,16 +133,22 @@ find examples -name .cvsignore -exec rm {} \;
 %dir %{_libdir}/ocaml/lablgtk2
 %{_libdir}/ocaml/lablgtk2/META
 %{_libdir}/ocaml/lablgtk2/*.a
+%if %{opt}
 %{_libdir}/ocaml/lablgtk2/*.cmxa
 %{_libdir}/ocaml/lablgtk2/*.cmx
+%endif
 %{_libdir}/ocaml/lablgtk2/*.mli
 %{_libdir}/ocaml/lablgtk2/*.ml
 %{_libdir}/ocaml/lablgtk2/*.h
 %{_libdir}/ocaml/lablgtk2/gtkInit.cmo
+%if %{opt}
 %{_libdir}/ocaml/lablgtk2/gtkInit.o
+%endif
 %{_libdir}/ocaml/lablgtk2/gtkThInit.cmo
 %{_libdir}/ocaml/lablgtk2/gtkThread.cmo
+%if %{opt}
 %{_libdir}/ocaml/lablgtk2/gtkThread.o
+%endif
 %{_libdir}/ocaml/lablgtk2/propcc
 %{_libdir}/ocaml/lablgtk2/varcc
 
@@ -145,6 +158,9 @@ find examples -name .cvsignore -exec rm {} \;
 
 
 %changelog
+* Wed Jul 22 2015 Richard W.M. Jones <rjones@redhat.com> - 2.18.3-6
+- Enable bytecode builds (patch supplied by Rafael Fonseca).
+
 * Tue Jul 07 2015 Richard W.M. Jones <rjones@redhat.com> - 2.18.3-5
 - Drop dependency on gtksourceview-devel.  See:
   https://lists.fedoraproject.org/pipermail/devel/2015-July/thread.html#212049