diff --git a/.gitignore b/.gitignore
index 893eeec1..731c935f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,7 @@ geckodriver.log
 
 # pyenv
 .python-version
+
+# codecov
+.coverage
+coverage.xml
diff --git a/CHANGELOG.md b/CHANGELOG.md
index feecccd7..82e4906f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,9 @@
   override `selenium_standalone` fixture with `selenium_standalone_refresh`.
   [#65](https://github.com/pyodide/pytest-pyodide/pull/65)
 
+- Breaking: `--runtime` commandline flag now requires runtimes to be comma-separated.
+  [#76](https://github.com/pyodide/pytest-pyodide/pull/76)
+
 - Add support for a custom `SimpleHTTPRequestHandler` class in the pytest
   webserver code, by passing the `handler_cls` parameter in the
   `spawn_web_server` function.
diff --git a/pytest_pyodide/hook.py b/pytest_pyodide/hook.py
index 0c401d5e..3b42cf3c 100644
--- a/pytest_pyodide/hook.py
+++ b/pytest_pyodide/hook.py
@@ -18,12 +18,25 @@
 RUNTIMES_NO_HOST = [f"{runtime}-no-host" for runtime in RUNTIMES]
 
 
-def _filter_runtimes(runtime: list[str]) -> tuple[bool, set[str]]:
+def _filter_runtimes(runtime: str) -> tuple[bool, set[str]]:
+    """Preprocess the given runtime commandline parameter
+
+    >>> _filter_runtimes("chrome")
+    (True, {'chrome'})
+    >>> _filter_runtimes("chrome-no-host")
+    (False, {'chrome'})
+    >>> _filter_runtimes("chrome-no-host, host, firefox")
+    (True, ...)
+    """
+
     # Always run host test, unless 'no-host' is given.
     run_host = True
 
+    # "chrome, firefox, node" ==> ["chrome", "firefox", "node"]
+    runtimes = [rt.strip() for rt in runtime.split(",")]
+
     # remove duplicates
-    runtime_set = set(runtime)
+    runtime_set = set(runtimes)
 
     runtime_filtered = set()
     for rt in runtime_set:
@@ -33,11 +46,15 @@ def _filter_runtimes(runtime: list[str]) -> tuple[bool, set[str]]:
 
         runtime_filtered.add(rt)
 
-    # If '--rt chrome-no-host --rt host' is given, we run host tests.
+    # If '--rt "chrome-no-host, host"' is given, we run host tests.
     run_host = run_host or ("host" in runtime_filtered)
 
     runtime_filtered.discard("host")
 
+    for rt in runtime_filtered:
+        if rt not in RUNTIMES:
+            raise ValueError(f"Invalid runtime: {rt}")
+
     return run_host, runtime_filtered
 
 
@@ -89,10 +106,8 @@ def pytest_addoption(parser):
         "--rt",
         "--runtime",
         dest="runtime",
-        nargs="+",
-        default=["node"],
-        choices=RUNTIMES_AND_HOST + RUNTIMES_NO_HOST,
-        help="Select runtime (default: %(default)s)",
+        default="node",
+        help="Select runtimes to run tests (default: %(default)s)",
     )
 
 
diff --git a/tests/test_options.py b/tests/test_options.py
index e7186d2c..e11c1574 100644
--- a/tests/test_options.py
+++ b/tests/test_options.py
@@ -56,20 +56,44 @@ def test_option(request):
         "firefox",
         "safari",
         "node",
-        "firefox chrome",
+        "firefox,chrome",
     ],
 )
 def test_runtime(pytester, _runtime):
 
-    runtimes = _runtime.split()
+    runtimes = _runtime.split(",")
 
     pytester.makepyfile(
         f"""
         import pytest
-        def test_option(request):
-            assert request.config.getoption("--runtime") == {runtimes!r}
+        def test_option():
+            assert pytest.pyodide_runtimes == set({runtimes!r})
         """
     )
 
-    result = pytester.runpytest("--runtime", *runtimes)
+    result = pytester.runpytest("--runtime", _runtime)
     result.assert_outcomes(passed=1)
+
+
+@pytest.mark.parametrize(
+    "_runtime",
+    [
+        "invalid",
+    ],
+)
+def test_invalid_runtime(pytester, _runtime):
+
+    runtimes = _runtime.split(",")
+
+    pytester.makepyfile(
+        f"""
+        import pytest
+        def test_option():
+            assert pytest.pyodide_runtimes == set({runtimes!r})
+        """
+    )
+
+    # TODO: catch internal errors directly?
+    with pytest.raises(ValueError, match="Pytest terminal summary report not found"):
+        result = pytester.runpytest("--runtime", _runtime)
+        result.assert_outcomes(errors=1)