diff --git a/tools/run_tests.py b/tools/run_tests.py
index 9847a6db8..444a2bec8 100755
--- a/tools/run_tests.py
+++ b/tools/run_tests.py
@@ -162,7 +162,7 @@ def debug_test_cases():
 
 
 def run_test_cases():
-    common.execute('stestr run --slowest {posargs}',
+    common.execute('stestr run {posargs}',
                    posargs=common.get_posargs(),
                    capture_stdout=False)
 
diff --git a/tox.ini b/tox.ini
index fa1cf35ea..c83de5d6d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -27,7 +27,7 @@ setenv =
     OS_TEST_PATH = {toxinidir}/tobiko/tests/unit
     PS1 = [tobiko@{envname}] {env:PS1:}
     PYTHONWARNINGS = ignore::Warning,{env:PYTHONWARNINGS:}
-    RUN_TESTS_EXTRA_ARGS =
+    RUN_TESTS_EXTRA_ARGS = --slowest
     TOBIKO_PREVENT_CREATE = {env:TOBIKO_PREVENT_CREATE:false}
     TOX_REPORT_NAME = {env:TOX_REPORT_NAME:test_results}
     TOX_REPORT_DIR = {env:TOX_REPORT_DIR:{toxinidir}/report/{envname}}
@@ -36,7 +36,7 @@ setenv =
     TOX_EXTRA_REQUIREMENTS = {env:TOX_EXTRA_REQUIREMENTS:-r{toxinidir}/extra-requirements.txt}
     VIRTUAL_ENV = {envdir}
 commands =
-    {envpython} {toxinidir}/tools/run_tests.py {env:RUN_TESTS_EXTRA_ARGS} {posargs}
+    {envpython} {toxinidir}/tools/run_tests.py {posargs:{env:RUN_TESTS_EXTRA_ARGS}}
 
 
 [testenv:py3]