diff --git a/academic/treebest-ensembl/treebest-ensembl.SlackBuild b/academic/treebest-ensembl/treebest-ensembl.SlackBuild
index b3a8844539..e4879d1cdc 100644
--- a/academic/treebest-ensembl/treebest-ensembl.SlackBuild
+++ b/academic/treebest-ensembl/treebest-ensembl.SlackBuild
@@ -2,7 +2,7 @@
 
 # Slackware build script for treebest
 
-# Copyright 2020 Petar Petrov slackalaxy@gmail.com
+# Copyright 2020-2021 Petar Petrov slackalaxy@gmail.com
 # All rights reserved.
 #
 # Redistribution and use of this script, with or without modification, is
@@ -76,10 +76,10 @@ find -L . \
 sed -i "/^CFLAGS/s/=/+=/" Makefile
 
 # Make the CLI treebest and the FLTK GUI
-CFLAGS="$SLKCFLAGS" \
+CFLAGS="$SLKCFLAGS -fcommon" \
 make
 
-CFLAGS="$SLKCFLAGS" \
+CFLAGS="$SLKCFLAGS -fcommon" \
 make fltreebest
 
 install -D -m755 treebest $PKG/usr/bin/treebest