diff --git a/Makefile b/Makefile
index c35398c..66af599 100644
--- a/Makefile
+++ b/Makefile
@@ -74,8 +74,7 @@ test-all: tox.ini## run tests on every Python version with tox
 	tox
 
 coverage: ## check code coverage quickly with the default Python
-	py.test --cov=abimap --cov-config .coveragerc --cov-report=term-missing -vv tests
-	coverage combine --append
+	py.test --cov=abimap --cov-append --cov-config .coveragerc --cov-report=term-missing -vv tests
 	coverage report
 	coverage html
 	$(BROWSER) htmlcov/index.html
diff --git a/ci/templates/tox.ini b/ci/templates/tox.ini
index 893b18d..79555ea 100644
--- a/ci/templates/tox.ini
+++ b/ci/templates/tox.ini
@@ -26,7 +26,7 @@ deps =
 commands =
     make bootstrap-tests
     nocov: {posargs:py.test -vv --ignore=src}
-    cover: {posargs:py.test --cov --cov-report=term-missing -vv}
+    cover: {posargs:py.test --cov --cov-append --cov-report=term-missing -vv}
 
 [testenv:bootstrap]
 deps =
@@ -97,7 +97,6 @@ deps = coverage
 skip_install = true
 usedevelop = false
 commands =
-    coverage combine --append
     coverage report
     coverage html
 
diff --git a/tox.ini b/tox.ini
index 194ec4e..9817d9e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -26,7 +26,7 @@ deps =
 commands =
     make bootstrap-tests
     nocov: {posargs:py.test -vv --ignore=src}
-    cover: {posargs:py.test --cov --cov-report=term-missing -vv}
+    cover: {posargs:py.test --cov --cov-append --cov-report=term-missing -vv}
 
 [testenv:bootstrap]
 deps =
@@ -97,7 +97,6 @@ deps = coverage
 skip_install = true
 usedevelop = false
 commands =
-    coverage combine --append
     coverage report
     coverage html