unsigned char blocksize_bits = inode->i_sb->s_blocksize_bits;
        unsigned long max_blocks = bh_result->b_size >> inode->i_blkbits;
        unsigned long len = bh_result->b_size;
-       unsigned int clusters_to_alloc = 0;
+       unsigned int clusters_to_alloc = 0, contig_clusters = 0;
 
        cpos = ocfs2_blocks_to_clusters(inode->i_sb, iblock);
 
                /* fill hole, allocate blocks can't be larger than the size
                 * of the hole */
                clusters_to_alloc = ocfs2_clusters_for_bytes(inode->i_sb, len);
-               if (clusters_to_alloc > contig_blocks)
-                       clusters_to_alloc = contig_blocks;
+               contig_clusters = ocfs2_clusters_for_blocks(inode->i_sb,
+                               contig_blocks);
+               if (clusters_to_alloc > contig_clusters)
+                       clusters_to_alloc = contig_clusters;
 
                /* allocate extent and insert them into the extent tree */
                ret = ocfs2_extend_allocation(inode, cpos,
 
        return (u64)clusters << c_to_b_bits;
 }
 
+static inline u32 ocfs2_clusters_for_blocks(struct super_block *sb,
+               u64 blocks)
+{
+       int b_to_c_bits = OCFS2_SB(sb)->s_clustersize_bits -
+                       sb->s_blocksize_bits;
+
+       blocks += (1 << b_to_c_bits) - 1;
+       return (u32)(blocks >> b_to_c_bits);
+}
+
 static inline u32 ocfs2_blocks_to_clusters(struct super_block *sb,
                                           u64 blocks)
 {