diff --git a/.travis.yml b/.travis.yml
index 74c25a6cf..7280a75f2 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,21 +6,16 @@ matrix:
     - { os: linux, env: PYTHON_VERSION=2.7 }
     - { os: linux, env: PYTHON_VERSION=3.6 }
     - { os: linux, env: PYTHON_VERSION=3.6 USE_OPENMP=false }
-    # - { os: osx, env: PYTHON_VERSION=3.6 }
+    - { os: osx, env: PYTHON_VERSION=3.6 }
 
 sudo: false
 
 before_install:
-  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
+  - if [ "$TRAVIS_OS_NAME" = "osx" ]; then
       brew tap homebrew/science;
-      brew update;
       brew install netcdf fftw;
-      export CXX=clang++;
-      export CC=clang;
       shell_session_update() { echo "Overriding shell_session_update"; };
-    else
-      export CXX=g++-6;
-      export CC=gcc-6;
+      sudo bash devtools/ci/install_gfortran.sh;
     fi
 
 addons:
@@ -31,8 +26,6 @@ addons:
     - gcc-6
     - g++-6
     - gfortran-6
-    - gfortran-5
-    - g++
     - gfortran
     - clang
     - libz-dev
@@ -50,10 +43,12 @@ install:
     - source devtools/ci/install_test.sh
 
 script:
-    - which gcc
-    - gcc -v
-    - which g++
-    - g++ -v
+    - if [ "$TRAVIS_OS_NAME" = "osx" ]; then
+          unset CC CXX;
+      else
+        export CXX=g++-6;
+        export CC=gcc-6;
+      fi
     - source devtools/travis-ci/install_pytraj.sh
     - source devtools/ci/run_tests.sh
 
diff --git a/devtools/ci/install_gfortran.sh b/devtools/ci/install_gfortran.sh
new file mode 100644
index 000000000..2e9bf47e7
--- /dev/null
+++ b/devtools/ci/install_gfortran.sh
@@ -0,0 +1,9 @@
+#!/bin/sh
+
+# osx
+# add linux too?
+gfortran_image=gfortran-6.1-ElCapitan
+wget http://coudert.name/software/${gfortran_image}.dmg
+hdiutil mount ${gfortran_image}.dmg
+installer -pkg /Volumes/${gfortran_image}/${gfortran_image}/gfortran.pkg -target /
+which gfortran
diff --git a/devtools/travis-ci/install_pytraj.sh b/devtools/travis-ci/install_pytraj.sh
index 848c80ccd..e1a321e02 100644
--- a/devtools/travis-ci/install_pytraj.sh
+++ b/devtools/travis-ci/install_pytraj.sh
@@ -9,7 +9,11 @@ else
     python=python
 fi
 
+# FIXME: remove
+# git clone https://github.com/Amber-MD/cpptraj
+# (cd cpptraj && git checkout d1d762564952d1a7df55126f5550a407b054f118)
 
+# use cpptraj master branch
 if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
     $python setup.py install --disable-openmp
 else