diff --git a/.gitignore b/.gitignore
index 280cb5e75..83c4055a5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -16,3 +16,5 @@ dist/
 examples/*.bin
 examples/*.tzx
 scratch/
+.coverage
+htmlcov/
diff --git a/tox.ini b/tox.ini
index f976526fe..a8b0b6975 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,9 +5,10 @@ envlist = py27,py36,pypy,flake8
 setenv = LANG=en_US.UTF-8
 deps =
     pytest
+    pytest-cov
     -rrequirements.txt
 commands =
-    py.test {posargs}
+    py.test --cov-report html --cov . {posargs}
 
 [flake8]
 max-line-length = 120