diff --git a/pmb/helpers/git.py b/pmb/helpers/git.py
index 7bdf5c97..4f1419b9 100644
--- a/pmb/helpers/git.py
+++ b/pmb/helpers/git.py
@@ -18,6 +18,7 @@ along with pmbootstrap.  If not, see <http://www.gnu.org/licenses/>.
 """
 import logging
 import os
+import shutil
 
 import pmb.build
 import pmb.chroot.apk
@@ -69,6 +70,11 @@ def clone(args, name_repo, shallow=True, chown_to_user=False):
 
 
 def rev_parse(args, revision="HEAD"):
+    if shutil.which("git") is None:
+        logging.warning("WARNING: Cannot determine revision of git " +
+                        "repository at " + args.aports + ". Command 'git' " +
+                        "not found.")
+        return ""
     rev = pmb.helpers.run.user(args, ["git", "rev-parse", revision],
                                args.aports, output_return=True, check=False)
     if rev is None:
diff --git a/pmb/install/file.py b/pmb/install/file.py
index 1d8c0b1d..b6c6d396 100644
--- a/pmb/install/file.py
+++ b/pmb/install/file.py
@@ -25,18 +25,21 @@ import pmb.helpers.git
 def write_os_release(args, suffix):
     logging.info("(" + suffix + ") write /etc/os-release")
     revision = pmb.helpers.git.rev_parse(args)
+    has_revision = revision != ""
     filepath = args.work + "/chroot_" + suffix + "/tmp/os-release"
     os_release = ('PRETTY_NAME="postmarketOS {version}"\n'
                   'NAME="postmarketOS"\n'
                   'VERSION_ID="{version}"\n'
-                  'VERSION="{version}-{hash:.8}"\n'
+                  'VERSION="{version}{sep}{hash:.8}"\n'
                   'ID="postmarketos"\n'
                   'ID_LIKE="alpine"\n'
                   'HOME_URL="https://www.postmarketos.org/"\n'
                   'SUPPORT_URL="https://gitlab.com/postmarketOS"\n'
                   'BUG_REPORT_URL="https://gitlab.com/postmarketOS/pmbootstrap/issues"\n'
-                  'PMOS_HASH="{hash}"\n'
-                  ).format(version=pmb.config.version, hash=revision)
+                  ).format(version=pmb.config.version,
+                           sep=("-" if has_revision else ""), hash=revision)
+    if has_revision:
+        os_release += ('PMOS_HASH="{hash}"\n').format(hash=revision)
     with open(filepath, "w") as handle:
         handle.write(os_release)
     pmb.chroot.root(args, ["mv", "/tmp/os-release", "/etc/os-release"], suffix)