diff --git a/meta/conf/distro/include/ptest-packagelists.inc b/meta/conf/distro/include/ptest-packagelists.inc
index 003348906a..674801d8b8 100644
--- a/meta/conf/distro/include/ptest-packagelists.inc
+++ b/meta/conf/distro/include/ptest-packagelists.inc
@@ -96,6 +96,7 @@ PTESTS_SLOW = "\
     libgcrypt \
     libmodule-build-perl \
     lttng-tools \
+    mdadm \
     openssh \
     openssl \
     parted \
@@ -119,7 +120,6 @@ PTESTS_PROBLEMS:append:x86 = " valgrind"
 #    rt-tests \ # Needs to be checked whether it runs at all
 #    bash \ # Test outcomes are non-deterministic by design
 #    ifupdown \ # Tested separately in lib/oeqa/selftest/cases/imagefeatures.py
-#    mdadm \ # Tests rely on non-deterministic sleep() amounts
 #    libinput \ # Tests need an unloaded system to be reliable
 #    libpam \ # Needs pam DISTRO_FEATURE
 #    numactl \ # qemu not (yet) configured for numa; all tests are skipped
@@ -132,7 +132,6 @@ PTESTS_PROBLEMS = "\
     rt-tests \
     bash \
     ifupdown \
-    mdadm \
     libinput \
     libpam \
     libseccomp \
diff --git a/meta/recipes-core/images/core-image-ptest.bb b/meta/recipes-core/images/core-image-ptest.bb
index 90c26641ba..ddc56c8f9f 100644
--- a/meta/recipes-core/images/core-image-ptest.bb
+++ b/meta/recipes-core/images/core-image-ptest.bb
@@ -19,6 +19,7 @@ BBCLASSEXTEND = "${@' '.join(['mcextend:'+x for x in d.getVar('PTESTS').split()]
 # strace-ptest in particular needs more than 500MB
 IMAGE_OVERHEAD_FACTOR = "1.0"
 IMAGE_ROOTFS_EXTRA_SPACE = "324288"
+IMAGE_ROOTFS_EXTRA_SPACE:virtclass-mcextend-mdadm = "1524288"
 IMAGE_ROOTFS_EXTRA_SPACE:virtclass-mcextend-strace = "1024288"
 IMAGE_ROOTFS_EXTRA_SPACE:virtclass-mcextend-lttng-tools = "1524288"