diff --git a/Build.c b/Build.c
index bb53a11..ff92cc1 100644
--- a/Build.c
+++ b/Build.c
@@ -204,16 +204,18 @@ int Build(char *mddev, int mdfd, int chunk, int level, int layout,
 			bitmap_fd = open(bitmap_file, O_RDWR);
 			if (bitmap_fd < 0) {
 				int major = BITMAP_MAJOR_HI;
+#if 0
 				if (bitmap_chunk == UnSet) {
 					fprintf(stderr, Name ": %s cannot be openned.",
 						bitmap_file);
 					return 1;
 				}
+#endif
 				if (vers < 9003) {
 					major = BITMAP_MAJOR_HOSTENDIAN;
 #ifdef __BIG_ENDIAN
 					fprintf(stderr, Name ": Warning - bitmaps created on this kernel are not portable\n"
-						"  between different architectured.  Consider upgrading the Linux kernel.\n");
+						"  between different architectures.  Consider upgrading the Linux kernel.\n");
 #endif
 				}
 				bitmapsize = size>>9; /* FIXME wrong for RAID10 */
diff --git a/ChangeLog b/ChangeLog
index 8e1d951..e4f4dad 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -5,6 +5,9 @@ Changes Prior to this release
 	DegradedArray) generates an Email.
     -   Assume "DEVICE partitions" if no DEVICE line is given.
     -   Support new 'offset' layout for raid10.
+    -   When creating a bitmap file, choose a chunksize to limit number
+	of bitmap chunks to 2 million.  More than this can cause kmalloc
+	failure.
 
 Changes Prior to 2.4.1 release
     -   Honour --write-mostly when adding to an array without persistent
diff --git a/Create.c b/Create.c
index df6d850..2cd644b 100644
--- a/Create.c
+++ b/Create.c
@@ -432,9 +432,6 @@ int Create(struct supertype *st, char *mddev, int mdfd,
 	if (bitmap_file) {
 		int uuid[4];
 
-		if (bitmap_chunk == UnSet)
-			bitmap_chunk = DEFAULT_BITMAP_CHUNK;
-
 		st->ss->uuid_from_super(uuid, super);
 		if (CreateBitmap(bitmap_file, force, (char*)uuid, bitmap_chunk,
 				 delay, write_behind,
diff --git a/Grow.c b/Grow.c
index bc8a73f..742f656 100644
--- a/Grow.c
+++ b/Grow.c
@@ -329,8 +329,6 @@ int Grow_addbitmap(char *devname, int fd, char *file, int chunk, int delay, int
 		int d;
 		int max_devs = st->max_devs;
 		void *super = NULL;
-		if (chunk == UnSet)
-			chunk = DEFAULT_BITMAP_CHUNK;
 
 		/* try to load a superblock */
 		for (d=0; d<max_devs; d++) {
diff --git a/bitmap.c b/bitmap.c
index 33deab1..75492f7 100644
--- a/bitmap.c
+++ b/bitmap.c
@@ -341,6 +341,17 @@ int CreateBitmap(char *filename, int force, char uuid[16],
 		return rv;
 	}
 
+	if (chunksize == UnSet) {
+		/* We don't want more than 2^21 chunks, as 2^11 fill up one
+		 * 4K page (2 bytes per chunk), and 2^10 address of those
+		 * fill up a 4K indexing page.  2^20 might be safer...
+		 */
+		chunksize = DEFAULT_BITMAP_CHUNK;
+		/* <<21 for 2^21 chunks, >>9 to convert bytes to sectors */
+		while (array_size > (chunksize << (21-9)))
+			chunksize <<= 1;
+	}
+
 	memset(&sb, 0, sizeof(sb));
 	sb.magic = BITMAP_MAGIC;
 	sb.version = major;
diff --git a/mdadm.8 b/mdadm.8
index 4ec2f76..57918bf 100644
--- a/mdadm.8
+++ b/mdadm.8
@@ -447,11 +447,12 @@ slash ('/') if it is a real file (not 'internal' or 'none').
 Note: external bitmaps are only known to work on ext2 and ext3.
 Storing bitmap files on other filesystems may result in serious problems.
 
-
 .TP
 .BR --bitmap-chunk=
 Set the chunksize of the bitmap. Each bit corresponds to that many
-Kilobytes of storage. Default is 4 when using a file based bitmap.
+Kilobytes of storage.
+When using a file based bitmap, the default is to use the smallest
+size that is atleast 4 and requires no more than 2^21 chunks.
 When using an
 .B internal
 bitmap, the chunksize is automatically determined to make best use of
diff --git a/mdadm.c b/mdadm.c
index f310474..7f10948 100644
--- a/mdadm.c
+++ b/mdadm.c
@@ -1020,7 +1020,6 @@ int main(int argc, char *argv[])
 		}
 		break;
 	case BUILD:
-		if (bitmap_chunk == UnSet) bitmap_chunk = DEFAULT_BITMAP_CHUNK;
 		if (delay == 0) delay = DEFAULT_BITMAP_DELAY;
 		if (write_behind && !bitmap_file) {
 			fprintf(stderr, Name ": write-behind mode requires a bitmap.\n");