diff --git a/kernel/blockio.c b/kernel/blockio.c
index 0c02db1..2840f2d 100644
--- a/kernel/blockio.c
+++ b/kernel/blockio.c
@@ -259,6 +259,24 @@ VOID setinvld(REG COUNT dsk)
   while (FP_OFF(bp) != FP_OFF(firstbuf));
 }
 
+/*      Check if there is at least one dirty buffer                     */
+/*                                                                      */
+BOOL dirty_buffers(REG COUNT dsk)
+{
+  struct buffer FAR *bp = firstbuf;
+
+  do
+  {
+    if (bp->b_unit == dsk &&
+        (bp->b_flag & (BFR_VALID | BFR_DIRTY)) == (BFR_VALID | BFR_DIRTY))
+      return TRUE;
+    bp = b_next(bp);
+  }
+  while (FP_OFF(bp) != FP_OFF(firstbuf));
+  return FALSE;
+}
+
+/*                                                                      */
 /*                                                                      */
 /*                      Flush all buffers for a disk                    */
 /*                                                                      */
diff --git a/kernel/fatfs.c b/kernel/fatfs.c
index c0efeaf..8fa565d 100644
--- a/kernel/fatfs.c
+++ b/kernel/fatfs.c
@@ -1687,8 +1687,10 @@ COUNT media_check(REG struct dpb FAR * dpbp)
       /* If it is forced or the media may have changed,       */
       /* rebuild the bpb                                      */
     case M_DONT_KNOW:
-        /* hazard: no error checking! */
-      flush_buffers(dpbp->dpb_unit);
+      /* IBM PCDOS technical reference says to call BLDBPB if */
+      /* there are no used buffers                            */
+      if (dirty_buffers(dpbp->dpb_unit))
+        return SUCCESS;
 
       /* If it definitely changed, don't know (falls through) */
       /* or has been changed, rebuild the bpb.                */
diff --git a/kernel/proto.h b/kernel/proto.h
index fa93118..7430b77 100644
--- a/kernel/proto.h
+++ b/kernel/proto.h
@@ -38,6 +38,7 @@ struct buffer FAR *getblk(ULONG blkno, COUNT dsk, BOOL overwrite);
 #define getblock(blkno, dsk) getblk(blkno, dsk, FALSE);
 #define getblockOver(blkno, dsk) getblk(blkno, dsk, TRUE);
 VOID setinvld(REG COUNT dsk);
+BOOL dirty_buffers(REG COUNT dsk);
 BOOL flush_buffers(REG COUNT dsk);
 BOOL flush(void);
 BOOL fill(REG struct buffer FAR * bp, ULONG blkno, COUNT dsk);