diff --git a/Makefile b/Makefile
index 578f6b1ae..cd8095ae1 100644
--- a/Makefile
+++ b/Makefile
@@ -16,7 +16,7 @@ test:
 	python -m unittest
 
 coverage:
-	coverage run --source websockets,tests -m unittest
+	coverage run --source src/websockets,tests -m unittest
 	coverage html
 	coverage report --show-missing --fail-under=100
 
diff --git a/tox.ini b/tox.ini
index 3a284ed31..2f37cdcbf 100644
--- a/tox.ini
+++ b/tox.ini
@@ -17,7 +17,7 @@ commands = python -W error::DeprecationWarning -W error::PendingDeprecationWarni
 [testenv:coverage]
 commands =
     python -m coverage erase
-    python -W default -m coverage run -m unittest {posargs}
+    python -m coverage run --source {envsitepackagesdir}/websockets,tests -m unittest {posargs}
     python -m coverage report --show-missing --fail-under=100
 deps = coverage