diff --git a/tox.ini b/tox.ini
index cbd3bd44..944e81be 100644
--- a/tox.ini
+++ b/tox.ini
@@ -11,8 +11,6 @@ requires =
     setuptools >= 30.3.0
     pip >= 19.3.1
 isolated_build = true
-indexserver =
-    NIGHTLY = https://pypi.anaconda.org/scipy-wheels-nightly/simple
 
 [testenv]
 
@@ -95,8 +93,8 @@ deps =
     astropy51: astropy==5.1.*
     astropy52: astropy==5.2.*
 
-    dev: :NIGHTLY:numpy
-    dev: :NIGHTLY:scipy
+    dev: numpy
+    dev: scipy
     dev: git+https://github.com/astropy/astropy.git#egg=astropy
 
     latest: astropy==5.2.*
@@ -121,6 +119,13 @@ commands =
     !cov: pytest --pyargs skypy {toxinidir}/docs {posargs}
     cov: pytest --pyargs skypy {toxinidir}/docs --cov skypy --cov-config={toxinidir}/setup.cfg {posargs}
 
+# For dev environment, use scipy-nightly-wheels as the default index server (for numpy and scipy)
+# and PyPI as the extra index server (for all other dependencies, except astropy which is installed
+# directly from GitHub).
+setenv =
+    dev: PIP_INDEX_URL = https://pypi.anaconda.org/scipy-wheels-nightly/simple
+    dev: PIP_EXTRA_INDEX_URL = https://pypi.org/simple
+
 [testenv:build_docs]
 changedir = docs
 description = invoke sphinx-build to build the HTML docs