diff --git a/sys/dev/mcd/mcd.c b/sys/dev/mcd/mcd.c
index 5ab40ef0761..37bd50842e5 100644
--- a/sys/dev/mcd/mcd.c
+++ b/sys/dev/mcd/mcd.c
@@ -296,6 +296,8 @@ int mcdopen(dev_t dev, int flags, int fmt, struct proc *p)
 	if (!(cd->flags & MCDVALID) && cd->openflags)
 		return ENXIO;
 
+	dev->si_bsize_phys = 2048;
+	dev->si_bsize_max = MAXBSIZE;
 	if (mcd_getstat(unit,1) == -1)
 		return EIO;
 
diff --git a/sys/dev/scd/scd.c b/sys/dev/scd/scd.c
index 5ec3eadead2..1742fdd4781 100644
--- a/sys/dev/scd/scd.c
+++ b/sys/dev/scd/scd.c
@@ -258,6 +258,8 @@ scdopen(dev_t dev, int flags, int fmt, struct proc *p)
 
 	XDEBUG(1,("scd%d: DEBUG: status = 0x%x\n", unit, inb(cd->iobase+IREG_STATUS)));
 
+	dev->si_bsize_phys = 2048;
+	dev->si_bsize_max = MAXBSIZE;
 	if ((rc = spin_up(unit)) != 0) {
 		print_error(unit, rc);
 		return EIO;
diff --git a/sys/i386/isa/atapi-cd.c b/sys/i386/isa/atapi-cd.c
index 72412a93133..a8adbab14ca 100644
--- a/sys/i386/isa/atapi-cd.c
+++ b/sys/i386/isa/atapi-cd.c
@@ -399,6 +399,8 @@ acdopen(dev_t dev, int flags, int fmt, struct proc *p)
         return ENXIO;
     cdp = acdtab[lun];
 
+    dev->si_bsize_phys = 2048;
+    dev->si_bsize_max = MAXBSIZE;
     if (!(cdp->flags & F_BOPEN) && !cdp->refcnt) {
         /* Prevent user eject */
         acd_request_wait(cdp, ATAPI_PREVENT_ALLOW,
diff --git a/sys/i386/isa/matcd/matcd.c b/sys/i386/isa/matcd/matcd.c
index a29d1b9b1e5..71b67da6739 100644
--- a/sys/i386/isa/matcd/matcd.c
+++ b/sys/i386/isa/matcd/matcd.c
@@ -623,6 +623,8 @@ int	matcdopen(dev_t dev, int flags, int fmt,
 
 	if (ldrive >= TOTALDRIVES) return(ENXIO);
 
+	dev->si_bsize_phys = 2048;
+	dev->si_bsize_max = MAXBSIZE;
 
 #ifdef DEBUGOPEN
 	printf("matcd%d: Open: dev %x partition %x controller %x flags %x cdrive %x\n",
diff --git a/sys/i386/isa/mcd.c b/sys/i386/isa/mcd.c
index 5ab40ef0761..37bd50842e5 100644
--- a/sys/i386/isa/mcd.c
+++ b/sys/i386/isa/mcd.c
@@ -296,6 +296,8 @@ int mcdopen(dev_t dev, int flags, int fmt, struct proc *p)
 	if (!(cd->flags & MCDVALID) && cd->openflags)
 		return ENXIO;
 
+	dev->si_bsize_phys = 2048;
+	dev->si_bsize_max = MAXBSIZE;
 	if (mcd_getstat(unit,1) == -1)
 		return EIO;
 
diff --git a/sys/i386/isa/scd.c b/sys/i386/isa/scd.c
index 5ec3eadead2..1742fdd4781 100644
--- a/sys/i386/isa/scd.c
+++ b/sys/i386/isa/scd.c
@@ -258,6 +258,8 @@ scdopen(dev_t dev, int flags, int fmt, struct proc *p)
 
 	XDEBUG(1,("scd%d: DEBUG: status = 0x%x\n", unit, inb(cd->iobase+IREG_STATUS)));
 
+	dev->si_bsize_phys = 2048;
+	dev->si_bsize_max = MAXBSIZE;
 	if ((rc = spin_up(unit)) != 0) {
 		print_error(unit, rc);
 		return EIO;
diff --git a/sys/i386/isa/wd_cd.c b/sys/i386/isa/wd_cd.c
index 72412a93133..a8adbab14ca 100644
--- a/sys/i386/isa/wd_cd.c
+++ b/sys/i386/isa/wd_cd.c
@@ -399,6 +399,8 @@ acdopen(dev_t dev, int flags, int fmt, struct proc *p)
         return ENXIO;
     cdp = acdtab[lun];
 
+    dev->si_bsize_phys = 2048;
+    dev->si_bsize_max = MAXBSIZE;
     if (!(cdp->flags & F_BOPEN) && !cdp->refcnt) {
         /* Prevent user eject */
         acd_request_wait(cdp, ATAPI_PREVENT_ALLOW,
diff --git a/sys/pc98/pc98/wd_cd.c b/sys/pc98/pc98/wd_cd.c
index 72412a93133..a8adbab14ca 100644
--- a/sys/pc98/pc98/wd_cd.c
+++ b/sys/pc98/pc98/wd_cd.c
@@ -399,6 +399,8 @@ acdopen(dev_t dev, int flags, int fmt, struct proc *p)
         return ENXIO;
     cdp = acdtab[lun];
 
+    dev->si_bsize_phys = 2048;
+    dev->si_bsize_max = MAXBSIZE;
     if (!(cdp->flags & F_BOPEN) && !cdp->refcnt) {
         /* Prevent user eject */
         acd_request_wait(cdp, ATAPI_PREVENT_ALLOW,