diff --git a/src/common.rs b/src/common.rs
index 3086efd..cf3d587 100644
--- a/src/common.rs
+++ b/src/common.rs
@@ -27,6 +27,13 @@ pub(crate) const FDT_NOP: u32 = 0x4;
 pub(crate) const FDT_END: u32 = 0x9;
 pub(crate) const SUPPORTED_VERSION: u32 = 17;
 
+// In spec 5.6:
+// Specifically, the memory reservation block shall
+// be aligned to an 8-byte boundary and the structure
+// block to a 4-byte boundary.
+pub(crate) const OFFSET_ALIGN: u32 = 64;
+pub(crate) const HEADER_PADDING_LEN: u32 = HEADER_LEN.div_ceil(OFFSET_ALIGN) * OFFSET_ALIGN;
+
 impl Header {
     pub fn verify(&self) -> Result<(), Error> {
         let header_base = self as *const _ as usize;
diff --git a/src/ser/mod.rs b/src/ser/mod.rs
index 3487562..0bc404e 100644
--- a/src/ser/mod.rs
+++ b/src/ser/mod.rs
@@ -19,49 +19,70 @@ where
 {
     writer.iter_mut().for_each(|x| *x = 0);
 
-    let mut offset: usize = 0;
-    {
-        let mut dst = crate::ser::pointer::Pointer::new(None);
-        let mut patch_list = crate::ser::patch::PatchList::new(list);
-        let mut block = crate::ser::string_block::StringBlock::new(writer, &mut offset);
-        let mut ser =
-            crate::ser::serializer::SerializerInner::new(&mut dst, &mut block, &mut patch_list);
-        let ser = crate::ser::serializer::Serializer::new(&mut ser);
-        data.serialize(ser)?;
+    let string_block_length = {
+        let mut offset: usize = 0;
+        {
+            let mut dst = crate::ser::pointer::Pointer::new(None);
+            let mut patch_list = crate::ser::patch::PatchList::new(list);
+            let mut block = crate::ser::string_block::StringBlock::new(writer, &mut offset);
+            let mut ser =
+                crate::ser::serializer::SerializerInner::new(&mut dst, &mut block, &mut patch_list);
+            let ser = crate::ser::serializer::Serializer::new(&mut ser);
+            data.serialize(ser)?;
+            offset
+        };
+        {
+            let mut block = crate::ser::string_block::StringBlock::new(writer, &mut offset);
+            block.align();
+        };
+        offset
     };
     list.iter().for_each(|patch| patch.init());
     // Write from bottom to top, to avoid overlap.
-    for i in (0..offset).rev() {
-        writer[writer.len() - offset + i] = writer[i];
+    for i in (0..string_block_length).rev() {
+        writer[writer.len() - string_block_length + i] = writer[i];
         writer[i] = 0;
     }
-    // TODO: make sure no out of bound.
 
-    let writer_len = writer.len();
-    let (data_block, string_block) = writer.split_at_mut(writer.len() - offset);
-    let (header, data_block) = data_block.split_at_mut(HEADER_LEN as usize + RSVMAP_LEN);
     let struct_len = {
+        let (data_block, string_block) = writer.split_at_mut(writer.len() - string_block_length);
+        let (_, data_block) = data_block.split_at_mut(HEADER_PADDING_LEN as usize + RSVMAP_LEN);
         let mut patch_list = crate::ser::patch::PatchList::new(list);
-        let mut block = crate::ser::string_block::StringBlock::new(string_block, &mut offset);
+        let mut temp_length = string_block_length;
+        let mut block = crate::ser::string_block::StringBlock::new(string_block, &mut temp_length);
         let mut dst = crate::ser::pointer::Pointer::new(Some(data_block));
         let mut ser =
             crate::ser::serializer::SerializerInner::new(&mut dst, &mut block, &mut patch_list);
         let ser = crate::ser::serializer::Serializer::new(&mut ser);
-        data.serialize(ser)?
+        let struct_len = data.serialize(ser)?.1;
+        assert_eq!(struct_len % 4, 0); // As spec, structure block align with 4 bytes.
+        assert_eq!(temp_length, string_block_length); // StringBlock should be same with first run.
+        struct_len
+    };
+
+    // Align to 8-bytes.
+    for i in 0..string_block_length {
+        writer[HEADER_PADDING_LEN as usize + RSVMAP_LEN + struct_len + i] =
+            writer[writer.len() - string_block_length + i];
+        writer[writer.len() - string_block_length + i] = 0;
     }
-    .1;
+
     // Make header
     {
+        let (header, _) = writer.split_at_mut(HEADER_LEN as usize);
         let header = unsafe { &mut *(header.as_mut_ptr() as *mut Header) };
         header.magic = u32::from_be(DEVICE_TREE_MAGIC);
-        header.total_size = u32::from_be(writer_len as u32);
-        header.off_dt_struct = u32::from_be(HEADER_LEN + RSVMAP_LEN as u32);
-        header.off_dt_strings = u32::from_be((writer_len - offset) as u32);
-        header.off_mem_rsvmap = u32::from_be(HEADER_LEN);
+        header.total_size = u32::from_be(
+            HEADER_PADDING_LEN + (RSVMAP_LEN + struct_len + string_block_length) as u32,
+        );
+        assert_eq!(header.total_size % 8, 0);
+        header.off_dt_struct = u32::from_be(HEADER_PADDING_LEN + RSVMAP_LEN as u32);
+        header.off_dt_strings = u32::from_be(HEADER_PADDING_LEN + (RSVMAP_LEN + struct_len) as u32);
+        header.off_mem_rsvmap = u32::from_be(HEADER_PADDING_LEN);
         header.version = u32::from_be(SUPPORTED_VERSION);
         header.last_comp_version = u32::from_be(SUPPORTED_VERSION); // TODO: maybe 16
-        header.boot_cpuid_phys = 0; // TODO: wtf is this prop
-        header.size_dt_strings = u32::from_be(offset as u32);
+        header.boot_cpuid_phys = 0; // TODO
+        header.size_dt_strings = u32::from_be(string_block_length as u32);
         header.size_dt_struct = u32::from_be(struct_len as u32);
     }
     Ok(())
diff --git a/src/ser/serializer.rs b/src/ser/serializer.rs
index 2b982f3..39b03d1 100644
--- a/src/ser/serializer.rs
+++ b/src/ser/serializer.rs
@@ -535,7 +535,7 @@ impl<'se> serde::ser::Serializer for Serializer<'_, 'se> {
 #[cfg(test)]
 mod tests {
     use serde::Serialize;
-    const MAX_SIZE: usize = 256 + 32;
+    const MAX_SIZE: usize = 256 + 128;
     #[test]
     fn base_ser_test() {
         #[derive(Serialize)]
diff --git a/src/ser/string_block.rs b/src/ser/string_block.rs
index af86434..672b7d3 100644
--- a/src/ser/string_block.rs
+++ b/src/ser/string_block.rs
@@ -51,6 +51,15 @@ impl<'se> StringBlock<'se> {
         result
     }
 
+    /// Align string block size to 8 bytes
+    #[inline(always)]
+    pub fn align(&mut self) {
+        while (*self.end & 0b111) != 0 {
+            self.data[*self.end] = 0;
+            *self.end += 1;
+        }
+    }
+
     /// Find a string. If not found, insert it.
     #[inline(always)]
     pub fn find_or_insert(&mut self, name: &str) -> usize {