diff --git a/libcontainers-common.changes b/libcontainers-common.changes
index 95a9b59..155db66 100644
--- a/libcontainers-common.changes
+++ b/libcontainers-common.changes
@@ -1,3 +1,8 @@
+-------------------------------------------------------------------
+Wed Jun 15 10:20:16 UTC 2022 - Fabian Vogt <fvogt@suse.com>
+
+- Use $() again in %post, but with a space for POSIX compliance
+
 -------------------------------------------------------------------
 Tue Jun 14 13:53:43 UTC 2022 - Dan Čermák <dcermak@suse.com>
 
diff --git a/libcontainers-common.spec b/libcontainers-common.spec
index 30ed54a..f712d36 100644
--- a/libcontainers-common.spec
+++ b/libcontainers-common.spec
@@ -139,7 +139,8 @@ sed -i 's/ostree_repo = ""/\#ostree_repo = ""/g' /etc/containers/storage.conf
 # If installing, check if /var/lib/containers (or /var/lib in its defect) is btrfs and set driver
 # to "btrfs" if true
 if [ $1 -eq 1 ] ; then
-  fstype=`(findmnt -o FSTYPE -l --target /var/lib/containers || findmnt -o FSTYPE -l --target /var/lib) | grep -v FSTYPE`
+  # Space to avoid ambiguity with arithmetic expansion
+  fstype=$( (findmnt -o FSTYPE -l --target /var/lib/containers || findmnt -o FSTYPE -l --target /var/lib) | grep -v FSTYPE)
   if [ "$fstype" = "btrfs" ]; then
     sed -i 's/driver = "overlay"/driver = "btrfs"/g' %{_sysconfdir}/containers/storage.conf
   fi