diff --git a/src/nspawn/nspawn-settings.h b/src/nspawn/nspawn-settings.h
index c786bf8c86..4e9cf3e315 100644
--- a/src/nspawn/nspawn-settings.h
+++ b/src/nspawn/nspawn-settings.h
@@ -56,9 +56,19 @@ typedef enum SettingsMask {
         SETTING_CPU_AFFINITY      = UINT64_C(1) << 20,
         SETTING_RLIMIT_FIRST      = UINT64_C(1) << 21, /* we define one bit per resource limit here */
         SETTING_RLIMIT_LAST       = UINT64_C(1) << (21 + _RLIMIT_MAX - 1),
-        _SETTINGS_MASK_ALL        = (UINT64_C(1) << (21 + _RLIMIT_MAX)) - 1
+        _SETTINGS_MASK_ALL        = (UINT64_C(1) << (21 + _RLIMIT_MAX)) - 1,
+        _FORCE_ENUM_WIDTH         = UINT64_MAX
 } SettingsMask;
 
+/* We want to use SETTING_RLIMIT_FIRST in shifts, so make sure it is really 64 bits
+ * when used in expressions. */
+#define SETTING_RLIMIT_FIRST ((uint64_t) SETTING_RLIMIT_FIRST)
+#define SETTING_RLIMIT_LAST ((uint64_t) SETTING_RLIMIT_LAST)
+
+assert_cc(sizeof(SettingsMask) == 8);
+assert_cc(sizeof(SETTING_RLIMIT_FIRST) == 8);
+assert_cc(sizeof(SETTING_RLIMIT_LAST) == 8);
+
 typedef struct Settings {
         /* [Run] */
         StartMode start_mode;