diff --git a/tox.ini b/tox.ini
index 0b57eb2..1b8a0fd 100644
--- a/tox.ini
+++ b/tox.ini
@@ -30,6 +30,7 @@
 [testenv:heat-slow]
 sitepackages = True
 setenv = VIRTUAL_ENV={envdir}
+         OS_TEST_TIMEOUT=1200
 # The regex below is used to select heat api/scenario tests tagged as slow.
 commands =
   sh tools/pretty_tox_serial.sh '(?=.*\[.*\bslow\b.*\])(^tempest\.(api|scenario)\.orchestration) {posargs}'