diff --git a/.coveragerc b/.coveragerc
index aa69fd4f5..a0a57b33a 100644
--- a/.coveragerc
+++ b/.coveragerc
@@ -4,6 +4,11 @@ source =
     cryptography
     tests/
 
+[paths]
+source =
+   src/cryptography
+   .tox/*/lib/python*/site-packages/cryptography
+
 [report]
 exclude_lines =
     @abc.abstractmethod
diff --git a/tox.ini b/tox.ini
index d47beac27..4d4ac20c1 100644
--- a/tox.ini
+++ b/tox.ini
@@ -11,7 +11,11 @@ deps =
     pytest
     ./vectors
 commands =
-    coverage run -m pytest --capture=no --strict {posargs}
+    # We use parallel mode and then combine here so that coverage.py will take
+    # the paths like .tox/py34/lib/python3.4/site-packages/cryptography/__init__.py
+    # and collapse them into src/cryptography/__init__.py.
+    coverage run --parallel-mode -m pytest --capture=no --strict {posargs}
+    coverage combine
     coverage report -m
 
 [testenv:docs]