diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index a8f617cf..46bc889f 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -6,6 +6,9 @@ on:
       - master
   pull_request: null
 
+env:
+  PY_COLORS: "1"
+
 jobs:
   tests:
     name: tests
@@ -31,6 +34,7 @@ jobs:
           access_token: ${{ github.token }}
 
       - uses: actions/checkout@v2
+
       - uses: conda-incubator/setup-miniconda@v2
         with:
           python-version: ${{ matrix.pyver }}
@@ -59,16 +63,34 @@ jobs:
           make install -j 4
           cd ..
 
-      - name: test bundled build
+      - name: test non-bundled build
         shell: bash -l {0}
         run: |
-          pip install -e . 
+          pip install -vv -e . \
+            --global-option="build_ext" \
+            --global-option="--use-system-fitsio" \
+            --global-option="--system-fitsio-includedir=$HOME/cfitsio-static-install/include" \
+            --global-option="--system-fitsio-libdir=$HOME/cfitsio-static-install/lib"
           SKIP_BZIP_TEST=true pytest -vv fitsio
 
-      - name: test non-bundled build
+      - name: test non-bundled build w/ env vars
+        shell: bash -l {0}
+        run: |
+          rm -rf build*
+          find . -name "*.so" -type f -delete
+          export FITSIO_USE_SYSTEM_FITSIO=1
+          export FITSIO_SYSTEM_FITSIO_INCLUDEDIR=$HOME/cfitsio-static-install/include
+          export FITSIO_SYSTEM_FITSIO_LIBDIR=$HOME/cfitsio-static-install/lib
+          pip install -vv -e .
+          SKIP_BZIP_TEST=true pytest -vv fitsio
+
+      - name: test bundled build
         shell: bash -l {0}
         run: |
-          pip install -e . --global-option="build_ext" --global-option "--use-system-fitsio"
+          rm -rf build*
+          rm -rf $HOME/cfitsio-static-install
+          find . -name "*.so" -type f -delete
+          pip install -vv -e .
           SKIP_BZIP_TEST=true pytest -vv fitsio
 
       - name: flake8
diff --git a/setup.py b/setup.py
index d2f6e4a1..669e7f0e 100644
--- a/setup.py
+++ b/setup.py
@@ -8,6 +8,7 @@
 from setuptools import setup, Extension, find_packages
 from setuptools.command.build_ext import build_ext
 
+import sys
 import os
 import subprocess
 from subprocess import Popen, PIPE
@@ -15,27 +16,60 @@
 import shutil
 
 
+if "--use-system-fitsio" in sys.argv:
+    del sys.argv[sys.argv.index("--use-system-fitsio")]
+    USE_SYSTEM_FITSIO = True
+else:
+    USE_SYSTEM_FITSIO = False or "FITSIO_USE_SYSTEM_FITSIO" in os.environ
+
+if (
+    "--system-fitsio-includedir" in sys.argv
+    or any(a.startswith("--system-fitsio-includedir=") for a in sys.argv)
+):
+    if "--system-fitsio-includedir" in sys.argv:
+        ind = sys.argv.index("--system-fitsio-includedir")
+        SYSTEM_FITSIO_INCLUDEDIR = sys.argv[ind+1]
+        del sys.argv[ind+1]
+        del sys.argv[ind]
+    else:
+        for ind in range(len(sys.argv)):
+            if sys.argv[ind].startswith("--system-fitsio-includedir="):
+                break
+        SYSTEM_FITSIO_INCLUDEDIR = sys.argv[ind].split("=", 1)[1]
+        del sys.argv[ind]
+else:
+    SYSTEM_FITSIO_INCLUDEDIR = os.environ.get(
+        "FITSIO_SYSTEM_FITSIO_INCLUDEDIR",
+        None,
+    )
+
+
+if (
+    "--system-fitsio-libdir" in sys.argv
+    or any(a.startswith("--system-fitsio-libdir=") for a in sys.argv)
+):
+    if "--system-fitsio-libdir" in sys.argv:
+        ind = sys.argv.index("--system-fitsio-libdir")
+        SYSTEM_FITSIO_LIBDIR = sys.argv[ind+1]
+        del sys.argv[ind+1]
+        del sys.argv[ind]
+    else:
+        for ind in range(len(sys.argv)):
+            if sys.argv[ind].startswith("--system-fitsio-libdir="):
+                break
+        SYSTEM_FITSIO_LIBDIR = sys.argv[ind].split("=", 1)[1]
+        del sys.argv[ind]
+else:
+    SYSTEM_FITSIO_LIBDIR = os.environ.get(
+        "FITSIO_SYSTEM_FITSIO_LIBDIR",
+        None,
+    )
+
+
 class build_ext_subclass(build_ext):
-    boolean_options = build_ext.boolean_options + ['use-system-fitsio']
-
-    user_options = build_ext.user_options + [
-        ('use-system-fitsio', None, "Use the cfitsio installed in the system"),
-        ('system-fitsio-includedir=', None,
-         "Path to look for cfitsio header; default is "
-         "the system search path."),
-        ('system-fitsio-libdir=', None,
-         "Path to look for cfitsio library; default is "
-         "the system search path."),
-    ]
     cfitsio_version = '3490'
     cfitsio_dir = 'cfitsio%s' % cfitsio_version
 
-    def initialize_options(self):
-        self.use_system_fitsio = False
-        self.system_fitsio_includedir = None
-        self.system_fitsio_libdir = None
-        build_ext.initialize_options(self)
-
     def finalize_options(self):
 
         build_ext.finalize_options(self)
@@ -47,11 +81,11 @@ def finalize_options(self):
         self.cfitsio_patch_dir = os.path.join(
             self.build_temp, 'patches')
 
-        if self.use_system_fitsio:
-            if self.system_fitsio_includedir:
-                self.include_dirs.insert(0, self.system_fitsio_includedir)
-            if self.system_fitsio_libdir:
-                self.library_dirs.insert(0, self.system_fitsio_libdir)
+        if USE_SYSTEM_FITSIO:
+            if SYSTEM_FITSIO_INCLUDEDIR is not None:
+                self.include_dirs.insert(0, SYSTEM_FITSIO_INCLUDEDIR)
+            if SYSTEM_FITSIO_LIBDIR is not None:
+                self.library_dirs.insert(0, SYSTEM_FITSIO_LIBDIR)
         else:
             # We defer configuration of the bundled cfitsio to build_extensions
             # because we will know the compiler there.
@@ -72,7 +106,7 @@ def run(self):
         build_ext.run(self)
 
     def build_extensions(self):
-        if not self.use_system_fitsio:
+        if not USE_SYSTEM_FITSIO:
 
             # Use the compiler for building python to build cfitsio
             # for maximized compatibility.