diff --git a/sbin/fsck_ffs/fsutil.c b/sbin/fsck_ffs/fsutil.c
index 48810954ba94..5e60aecf1826 100644
--- a/sbin/fsck_ffs/fsutil.c
+++ b/sbin/fsck_ffs/fsutil.c
@@ -1038,7 +1038,7 @@ check_cgmagic(int cg, struct bufarea *cgbp)
 		CHK(cgp->cg_ndblk, !=, sblock.fs_size - cgbase(&sblock, cg),
 		    "%jd");
 	}
-	start = &cgp->cg_space[0] - (u_char *)(&cgp->cg_firstfield);
+	start = sizeof(*cgp);
 	if (sblock.fs_magic == FS_UFS2_MAGIC) {
 		CHK(cgp->cg_iusedoff, !=, start, "%jd");
 	} else if (sblock.fs_magic == FS_UFS1_MAGIC) {
@@ -1098,7 +1098,7 @@ rebuild_cg(int cg, struct bufarea *cgbp)
 		cgp->cg_ndblk = sblock.fs_fpg;
 	else
 		cgp->cg_ndblk = sblock.fs_size - cgbase(&sblock, cg);
-	start = &cgp->cg_space[0] - (u_char *)(&cgp->cg_firstfield);
+	start = sizeof(*cgp);
 	if (sblock.fs_magic == FS_UFS2_MAGIC) {
 		cgp->cg_iusedoff = start;
 	} else if (sblock.fs_magic == FS_UFS1_MAGIC) {
diff --git a/sbin/fsck_ffs/pass5.c b/sbin/fsck_ffs/pass5.c
index 61be54ed54ed..58143a0e8211 100644
--- a/sbin/fsck_ffs/pass5.c
+++ b/sbin/fsck_ffs/pass5.c
@@ -116,7 +116,7 @@ pass5(void)
 			}
 		}
 	}
-	basesize = &newcg->cg_space[0] - (u_char *)(&newcg->cg_firstfield);
+	basesize = sizeof(*newcg);
 	if (sblock.fs_magic == FS_UFS2_MAGIC) {
 		newcg->cg_iusedoff = basesize;
 	} else {
@@ -131,7 +131,7 @@ pass5(void)
 		    fs->fs_old_cpg * sizeof(int32_t);
 		newcg->cg_iusedoff = newcg->cg_old_boff +
 		    fs->fs_old_cpg * fs->fs_old_nrpos * sizeof(u_int16_t);
-		memset(&newcg->cg_space[0], 0, newcg->cg_iusedoff - basesize);
+		memset(&newcg[1], 0, newcg->cg_iusedoff - basesize);
 	}
 	inomapsize = howmany(fs->fs_ipg, CHAR_BIT);
 	newcg->cg_freeoff = newcg->cg_iusedoff + inomapsize;
diff --git a/sbin/growfs/growfs.c b/sbin/growfs/growfs.c
index 93a51d03b18d..51bf997406d0 100644
--- a/sbin/growfs/growfs.c
+++ b/sbin/growfs/growfs.c
@@ -338,7 +338,7 @@ initcg(int cylno, time_t modtime, int fso, unsigned int Nflag)
 	acg.cg_ndblk = dmax - cbase;
 	if (sblock.fs_contigsumsize > 0)
 		acg.cg_nclusterblks = acg.cg_ndblk / sblock.fs_frag;
-	start = &acg.cg_space[0] - (u_char *)(&acg.cg_firstfield);
+	start = sizeof(acg);
 	if (sblock.fs_magic == FS_UFS2_MAGIC) {
 		acg.cg_iusedoff = start;
 	} else {
diff --git a/sbin/newfs/mkfs.c b/sbin/newfs/mkfs.c
index d8580a789b1d..adc64f47cac6 100644
--- a/sbin/newfs/mkfs.c
+++ b/sbin/newfs/mkfs.c
@@ -721,7 +721,7 @@ initcg(int cylno, time_t utime)
 	acg.cg_ndblk = dmax - cbase;
 	if (sblock.fs_contigsumsize > 0)
 		acg.cg_nclusterblks = acg.cg_ndblk / sblock.fs_frag;
-	start = &acg.cg_space[0] - (u_char *)(&acg.cg_firstfield);
+	start = sizeof(acg);
 	if (Oflag == 2) {
 		acg.cg_iusedoff = start;
 	} else {
@@ -749,7 +749,8 @@ initcg(int cylno, time_t utime)
 		    howmany(fragstoblks(&sblock, sblock.fs_fpg), CHAR_BIT);
 	}
 	if (acg.cg_nextfreeoff > (unsigned)sblock.fs_cgsize) {
-		printf("Panic: cylinder group too big\n");
+		printf("Panic: cylinder group too big by %d bytes\n",
+		    acg.cg_nextfreeoff - (unsigned)sblock.fs_cgsize);
 		exit(37);
 	}
 	acg.cg_cs.cs_nifree += sblock.fs_ipg;
diff --git a/sys/ufs/ffs/fs.h b/sys/ufs/ffs/fs.h
index c2279c183fc5..7b7a1f9f2ef6 100644
--- a/sys/ufs/ffs/fs.h
+++ b/sys/ufs/ffs/fs.h
@@ -573,11 +573,11 @@ CTASSERT(sizeof(struct fs) == 1376);
  * cylinder group and the (struct cg) size.
  */
 #define	CGSIZE(fs) \
-    /* base cg */	(sizeof(struct cg) + sizeof(int32_t) + \
+    /* base cg */	(sizeof(struct cg) + \
     /* old btotoff */	(fs)->fs_old_cpg * sizeof(int32_t) + \
     /* old boff */	(fs)->fs_old_cpg * sizeof(u_int16_t) + \
     /* inode map */	howmany((fs)->fs_ipg, NBBY) + \
-    /* block map */	howmany((fs)->fs_fpg, NBBY) +\
+    /* block map */	howmany((fs)->fs_fpg, NBBY) + sizeof(int32_t) + \
     /* if present */	((fs)->fs_contigsumsize <= 0 ? 0 : \
     /* cluster sum */	(fs)->fs_contigsumsize * sizeof(int32_t) + \
     /* cluster map */	howmany(fragstoblks(fs, (fs)->fs_fpg), NBBY)))
@@ -624,8 +624,7 @@ struct cg {
 	u_int32_t cg_ckhash;		/* check-hash of this cg */
 	ufs_time_t cg_time;		/* time last written */
 	int64_t	 cg_sparecon64[3];	/* reserved for future use */
-	u_int8_t cg_space[1];		/* space for cylinder group maps */
-/* actually longer */
+	/* actually longer - space used for cylinder group maps */
 };
 
 /*
diff --git a/usr.sbin/makefs/ffs/mkfs.c b/usr.sbin/makefs/ffs/mkfs.c
index ef745fe3c196..d48dc65aac68 100644
--- a/usr.sbin/makefs/ffs/mkfs.c
+++ b/usr.sbin/makefs/ffs/mkfs.c
@@ -634,7 +634,7 @@ initcg(uint32_t cylno, time_t utime, const fsinfo_t *fsopts)
 	acg.cg_ndblk = dmax - cbase;
 	if (sblock.fs_contigsumsize > 0)
 		acg.cg_nclusterblks = acg.cg_ndblk >> sblock.fs_fragshift;
-	start = &acg.cg_space[0] - (u_char *)(&acg.cg_firstfield);
+	start = sizeof(acg);
 	if (Oflag == 2) {
 		acg.cg_iusedoff = start;
 	} else {