diff --git a/stack.sh b/stack.sh
index 83da1c61cb..a0163701f0 100755
--- a/stack.sh
+++ b/stack.sh
@@ -1259,8 +1259,13 @@ if is_service_enabled g-reg; then
 fi
 
 # Create a randomized default value for the key manager's fixed_key
+# NOTE(lyarwood): This is currently set to 36 as a workaround to the following
+# libvirt bug that incorrectly pads passphrases that are a multiple of 16 bytes
+# in length.
+# Unable to use LUKS passphrase that is exactly 16 bytes long
+# https://bugzilla.redhat.com/show_bug.cgi?id=1447297
 if is_service_enabled nova; then
-    iniset $NOVA_CONF key_manager fixed_key $(generate_hex_string 32)
+    iniset $NOVA_CONF key_manager fixed_key $(generate_hex_string 36)
 fi
 
 # Launch the nova-api and wait for it to answer before continuing