diff --git a/fs/udf/balloc.c b/fs/udf/balloc.c
index 8c0c279..3f67d9d 100644
--- a/fs/udf/balloc.c
+++ b/fs/udf/balloc.c
@@ -231,9 +231,7 @@
 		block_count = part_len - first_block;
 
 repeat:
-	nr_groups = (sbi->s_partmaps[partition].s_partition_len +
-		     (sizeof(struct spaceBitmapDesc) << 3) +
-		     (sb->s_blocksize * 8) - 1) / (sb->s_blocksize * 8);
+	nr_groups = udf_compute_nr_groups(sb, partition);
 	block = first_block + (sizeof(struct spaceBitmapDesc) << 3);
 	block_group = block >> (sb->s_blocksize_bits + 3);
 	group_start = block_group ? 0 : sizeof(struct spaceBitmapDesc);
diff --git a/fs/udf/super.c b/fs/udf/super.c
index 86aa223..c19ee38 100644
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -937,18 +937,22 @@
 		  root->logicalBlockNum, root->partitionReferenceNum);
 }
 
+int udf_compute_nr_groups(struct super_block *sb, u32 partition)
+{
+	struct udf_part_map *map = &UDF_SB(sb)->s_partmaps[partition];
+	return (map->s_partition_len +
+		(sizeof(struct spaceBitmapDesc) << 3) +
+		(sb->s_blocksize * 8) - 1) /
+		(sb->s_blocksize * 8);
+}
+
 static struct udf_bitmap *udf_sb_alloc_bitmap(struct super_block *sb, u32 index)
 {
-	struct udf_part_map *map = &UDF_SB(sb)->s_partmaps[index];
 	struct udf_bitmap *bitmap;
 	int nr_groups;
 	int size;
 
-	/* TODO: move calculating of nr_groups into helper function */
-	nr_groups = (map->s_partition_len +
-			(sizeof(struct spaceBitmapDesc) << 3) +
-			(sb->s_blocksize * 8) - 1) /
-			(sb->s_blocksize * 8);
+	nr_groups = udf_compute_nr_groups(sb, index);
 	size = sizeof(struct udf_bitmap) +
 		(sizeof(struct buffer_head *) * nr_groups);
 
diff --git a/fs/udf/udf_sb.h b/fs/udf/udf_sb.h
index 2c05f82..d9adb0f 100644
--- a/fs/udf/udf_sb.h
+++ b/fs/udf/udf_sb.h
@@ -43,6 +43,8 @@
 
 struct logicalVolIntegrityDescImpUse *udf_sb_lvidiu(struct udf_sb_info *sbi);
 
+int udf_compute_nr_groups(struct super_block *sb, u32 partition);
+
 #define UDF_QUERY_FLAG(X,Y)			( UDF_SB(X)->s_flags & ( 1 << (Y) ) )
 #define UDF_SET_FLAG(X,Y)			( UDF_SB(X)->s_flags |= ( 1 << (Y) ) )
 #define UDF_CLEAR_FLAG(X,Y)			( UDF_SB(X)->s_flags &= ~( 1 << (Y) ) )