diff --git a/setup.py b/setup.py
index 13e01ccc..779cdf41 100644
--- a/setup.py
+++ b/setup.py
@@ -38,7 +38,8 @@ INSTALL_REQUIRES = []
 EXTRAS_REQUIRE = {
     "docs": ["sphinx", "zope.interface"],
     "tests": [
-        "coverage[toml]",
+        # 5.0 introduced toml; parallel was broken until 5.0.2
+        "coverage[toml]>=5.0.2",
         "hypothesis",
         "pympler",
         "pytest>=4.3.0",  # 4.3.0 dropped last use of `convert`
diff --git a/tox.ini b/tox.ini
index c53938d9..d0e79665 100644
--- a/tox.ini
+++ b/tox.ini
@@ -50,7 +50,7 @@ commands = coverage run -m pytest {posargs}
 [testenv:coverage-report]
 basepython = python3.7
 skip_install = true
-deps = coverage[toml]
+deps = coverage[toml]>=5.0.2
 commands =
     coverage combine
     coverage report