diff --git a/tox.ini b/tox.ini
index c98e12d15a..1a659da4e6 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,7 +5,7 @@ envlist =
     build_doc
     add-ons
 skip_missing_interpreters = true
-isolated_build = true
+isolated_build = platform_system!="Darwin"  # pymssql is installed before tox runs
 
 [testenv]
 # https://tox.wiki/en/latest/config.html#download
@@ -25,6 +25,9 @@ setenv =
     # set coverage output and project config
     COVERAGE_FILE = {toxinidir}/.coverage
     COVERAGE_RCFILE = {toxinidir}/.coveragerc
+allowlist_externals =
+    brew
+    export
 deps =
     pyqt5==5.12.*;platform_system=="Windows" and python_version<'3.10'
     pyqt5==5.15.*;platform_system!="Windows" or python_version>='3.10'
@@ -32,7 +35,7 @@ deps =
     pyqtwebengine==5.15.*;platform_system!="Windows" or python_version>='3.10'
     coverage
     psycopg2-binary
-    pymssql;platform_system!="Darwin" or python_version>="3.11"
+    #pymssql;platform_system!="Darwin" or python_version >= "3.11"
     latest: https://github.com/biolab/orange-canvas-core/archive/refs/heads/master.zip#egg=orange-canvas-core
     latest: https://github.com/biolab/orange-widget-base/archive/refs/heads/master.zip#egg=orange-widget-base
     # GUI requirements
@@ -69,6 +72,11 @@ deps =
     # oldest: xlsxwriter
 
 commands_pre =
+    brew install FreeTDS
+    #export CFLAGS="-I$(brew --prefix openssl)/include  -I$(brew --prefix freetds)/include"
+    #export LDFLAGS="-L$(brew --prefix openssl)/lib  -L$(brew --prefix freetds)/lib"
+    #export CPPFLAGS="-I$(brew --prefix openssl)/include -I$(brew --prefix freetds)/include"
+    pip install --pre --no-binary :all: pymssql --force
     # Verify installed packages have compatible dependencies
     pip check
     # freeze environment