diff --git a/sys/fs/msdosfs/msdosfs_vnops.c b/sys/fs/msdosfs/msdosfs_vnops.c
--- a/sys/fs/msdosfs/msdosfs_vnops.c
+++ b/sys/fs/msdosfs/msdosfs_vnops.c
@@ -1962,6 +1962,8 @@
 {
 	struct denode *dep;
 	struct defid *defhp;
+	_Static_assert(sizeof(struct defid) <= sizeof(struct fid),
+	    "struct defid cannot be larger than struct fid");
 
 	dep = VTODE(ap->a_vp);
 	defhp = (struct defid *)ap->a_fhp;
diff --git a/sys/fs/tmpfs/tmpfs_vnops.c b/sys/fs/tmpfs/tmpfs_vnops.c
--- a/sys/fs/tmpfs/tmpfs_vnops.c
+++ b/sys/fs/tmpfs/tmpfs_vnops.c
@@ -1709,6 +1709,8 @@
 	struct tmpfs_fid_data tfd;
 	struct tmpfs_node *node;
 	struct fid *fhp;
+	_Static_assert(sizeof(struct tmpfs_fid_data) <= sizeof(struct fid),
+	    "struct tmpfs_fid_data cannot be larger than struct fid");
 
 	node = VP_TO_TMPFS_NODE(ap->a_vp);
 	fhp = ap->a_fhp;
diff --git a/sys/fs/udf/udf_vnops.c b/sys/fs/udf/udf_vnops.c
--- a/sys/fs/udf/udf_vnops.c
+++ b/sys/fs/udf/udf_vnops.c
@@ -1274,6 +1274,8 @@
 {
 	struct udf_node *node;
 	struct ifid *ifhp;
+	_Static_assert(sizeof(struct ifid) <= sizeof(struct fid),
+	    "struct ifid cannot be larger than struct fid");
 
 	node = VTON(a->a_vp);
 	ifhp = (struct ifid *)a->a_fhp;
diff --git a/sys/ufs/ffs/ffs_vnops.c b/sys/ufs/ffs/ffs_vnops.c
--- a/sys/ufs/ffs/ffs_vnops.c
+++ b/sys/ufs/ffs/ffs_vnops.c
@@ -1919,6 +1919,8 @@
 {
 	struct inode *ip;
 	struct ufid *ufhp;
+	_Static_assert(sizeof(struct ufid) <= sizeof(struct fid),
+	    "struct ufid cannot be larger than struct fid");
 
 	ip = VTOI(ap->a_vp);
 	ufhp = (struct ufid *)ap->a_fhp;