diff --git a/libemile/emile_scsi_create_container.c b/libemile/emile_scsi_create_container.c
index 6e4b0fd..74d8506 100644
--- a/libemile/emile_scsi_create_container.c
+++ b/libemile/emile_scsi_create_container.c
@@ -39,7 +39,7 @@ static int get_scsi_path(int fd, unsigned char *host, unsigned char *channel,
 	return ret;
 }
 
-static int get_device_info(int fd, int *id, unsigned long *first_block, 
+static int get_device_info(int fd, short *id, unsigned long *first_block, 
 				       int *block_size)
 {
 	int ret;
@@ -101,11 +101,11 @@ static int get_device_info(int fd, int *id, unsigned long *first_block,
 		return -1;				\
 	}
 
-int emile_scsi_create_container(int fd, struct emile_container* container, int maxblocks)
+int emile_scsi_create_container(int fd, short *unit_id, 
+				struct emile_container* container, int maxblocks)
 {
 	int ret;
 	struct stat st;
-	int id;
 	unsigned long first_block;
 	int sector_size;
 	int block_size;
@@ -123,12 +123,11 @@ int emile_scsi_create_container(int fd, struct emile_container* container, int m
 		return -1;
 	}
 
-	ret = get_device_info(fd, &id, &first_block, &sector_size);
+	ret = get_device_info(fd, unit_id, &first_block, &sector_size);
 	if (ret != 0)
 		return -1;
 
 	container->size = st.st_size;
-	container->unit_id = (u_int16_t)id;
 
 	/* get filesystem block size */
 
diff --git a/libemile/emile_second_create_mapfile.c b/libemile/emile_second_create_mapfile.c
index 7ca554c..c9fb661 100644
--- a/libemile/emile_second_create_mapfile.c
+++ b/libemile/emile_second_create_mapfile.c
@@ -14,11 +14,12 @@
 
 #define MAPFILE_SIZE	4096
 
-struct emile_container *emile_second_create_mapfile(char *mapfile, char* kernel)
+struct emile_container *emile_second_create_mapfile(short *unit_id, char *mapfile, char* kernel)
 {
 	struct emile_container *container;
 	int fd;
 	int ret;
+	short unit_id_map;
 
 	container = (struct emile_container *)malloc(MAPFILE_SIZE);
 	if (container == NULL)
@@ -37,7 +38,7 @@ struct emile_container *emile_second_create_mapfile(char *mapfile, char* kernel)
 		return NULL;
 	}
 
-	ret = emile_scsi_create_container(fd, container, 
+	ret = emile_scsi_create_container(fd, &unit_id_map, container, 
 			(MAPFILE_SIZE - sizeof(struct emile_container)) / sizeof(struct emile_block));
 	close(fd);
 
@@ -79,7 +80,7 @@ struct emile_container *emile_second_create_mapfile(char *mapfile, char* kernel)
 		return NULL;
 	}
 
-	ret = emile_scsi_create_container(fd, container, 
+	ret = emile_scsi_create_container(fd, unit_id, container, 
 			(MAPFILE_SIZE - sizeof(struct emile_container)) / sizeof(struct emile_block));
 	close(fd);
 
@@ -90,6 +91,13 @@ struct emile_container *emile_second_create_mapfile(char *mapfile, char* kernel)
 		return NULL;
 	}
 
+	if (unit_id_map != *unit_id)
+	{
+		fprintf(stderr, "ERROR: map file must be on the same disk as the file to map\n");
+		free(container);
+		return NULL;
+	}
+
 	if (container->size != MAPFILE_SIZE)
 	{
 		fprintf(stderr, "ERROR: map file size is bad (%d)\n", container->size);
diff --git a/libemile/libemile.h b/libemile/libemile.h
index 39c1bdc..b59b627 100644
--- a/libemile/libemile.h
+++ b/libemile/libemile.h
@@ -71,11 +71,11 @@ extern int emile_first_set_param(int fd, unsigned short tune_mask,
 extern int emile_first_get_param(int fd, int *drive_num, int *second_offset, 
 				 int *second_size);
 extern int emile_first_set_param_scsi(int fd, char *second_name);
-struct emile_container *emile_second_create_mapfile(char *mapfile, char* kernel);
+struct emile_container *emile_second_create_mapfile(short *unit_id, char *mapfile, char* kernel);
 extern int emile_floppy_create_image(char* first_level, char* second_level, 
 				     char* kernel_image, char* ramdisk, 
 				     char* image);
-extern int emile_scsi_create_container(int fd, 
+extern int emile_scsi_create_container(int fd, short *unit_id,
 				       struct emile_container* container, int maxbloks);
 extern emile_map_t* emile_map_open(char* dev, int flags);
 extern void emile_map_close(emile_map_t *map);
diff --git a/tools/emile.c b/tools/emile.c
index 203f7f9..ba0accc 100644
--- a/tools/emile.c
+++ b/tools/emile.c
@@ -689,9 +689,10 @@ int main(int argc, char **argv)
 	{
 		char *configuration;
 		struct emile_container *container;
+		short unit_id;
 		char map_info[64];
 
-		container = emile_second_create_mapfile(map_path, kernel_path);
+		container = emile_second_create_mapfile(&unit_id, map_path, kernel_path);
 		if (container == NULL)
 		{
 			fprintf(stderr, 
@@ -707,7 +708,7 @@ int main(int argc, char **argv)
 
 		/* set kernel info */
 
-		sprintf(map_info, "container:(sd%d)0x%x,0x%x", container->unit_id, 
+		sprintf(map_info, "container:(sd%d)0x%x,0x%x", unit_id, 
 				   container->blocks[0].offset, container->blocks[0].count);
 		emile_second_set_property(configuration, "kernel", map_info);