diff --git a/tox.ini b/tox.ini
index 60e78c508..b6625e7a3 100644
--- a/tox.ini
+++ b/tox.ini
@@ -25,7 +25,8 @@ commands =
     coverage: coverage report
 passenv = USER USERNAME COVERAGE_* TRAVIS
 setenv =
-    # configuration if a user runs tox with a "coverage" factor, for example "tox -e py37-coverage"
+    # Configuration to run with coverage similar to Travis/Appveyor, e.g.
+    # "tox -e py37-coverage".
     coverage: _PYTEST_TOX_COVERAGE_RUN=coverage run -m
     coverage: _PYTEST_TOX_EXTRA_DEP=coverage-enable-subprocess
     coverage: COVERAGE_FILE={toxinidir}/.coverage
@@ -52,8 +53,8 @@ commands = pre-commit run --all-files --show-diff-on-failure
 [testenv:py27-xdist]
 extras = testing
 deps =
+    {[testenv]deps}
     pytest-xdist>=1.13
-    {env:_PYTEST_TOX_EXTRA_DEP:}
 commands =
     {env:_PYTEST_TOX_COVERAGE_RUN:} pytest -n auto {posargs}
 
@@ -61,15 +62,15 @@ commands =
 # NOTE: copied from above due to https://github.com/tox-dev/tox/issues/706.
 extras = testing
 deps =
+    {[testenv]deps}
     pytest-xdist>=1.13
-    {env:_PYTEST_TOX_EXTRA_DEP:}
 commands = {[testenv:py27-xdist]commands}
 
 [testenv:py27-pexpect]
 platform = linux|darwin
 deps =
+    {[testenv]deps}
     pexpect
-    {env:_PYTEST_TOX_EXTRA_DEP:}
 commands =
     {env:_PYTEST_TOX_COVERAGE_RUN:} pytest {posargs:testing/test_pdb.py testing/test_terminal.py testing/test_unittest.py}
 
@@ -81,8 +82,8 @@ commands = {[testenv:py27-pexpect]commands}
 [testenv:py27-nobyte]
 extras = testing
 deps =
+    {[testenv]deps}
     pytest-xdist>=1.13
-    {env:_PYTEST_TOX_EXTRA_DEP:}
 distribute = true
 setenv =
     {[testenv]setenv}
@@ -92,8 +93,8 @@ commands =
 
 [testenv:py27-trial]
 deps =
+    {[testenv]deps}
     twisted
-    {env:_PYTEST_TOX_EXTRA_DEP:}
 commands =
     {env:_PYTEST_TOX_COVERAGE_RUN:} pytest {posargs:testing/test_unittest.py}
 
@@ -103,8 +104,8 @@ commands = {[testenv:py27-trial]commands}
 
 [testenv:py27-numpy]
 deps =
+    {[testenv]deps}
     numpy
-    {env:_PYTEST_TOX_EXTRA_DEP:}
 commands=
   {env:_PYTEST_TOX_COVERAGE_RUN:} pytest {posargs:testing/python/approx.py}
 
@@ -138,8 +139,8 @@ commands =
 basepython = python3
 skipsdist = True
 deps =
+    {[testenv]deps}
     PyYAML
-    {env:_PYTEST_TOX_EXTRA_DEP:}
 commands =
     {env:_PYTEST_TOX_COVERAGE_RUN:} pytest doc/en
     {env:_PYTEST_TOX_COVERAGE_RUN:} pytest --doctest-modules --pyargs _pytest