diff --git a/androscalpel/src/dex_writer.rs b/androscalpel/src/dex_writer.rs
index 7f5b97a..822be15 100644
--- a/androscalpel/src/dex_writer.rs
+++ b/androscalpel/src/dex_writer.rs
@@ -1306,7 +1306,9 @@ impl DexWriter {
         let debug_info_off = if code.debug_info.is_empty() {
             0
         } else {
-            let debug_info_off = self.section_manager.get_size(Section::DebugInfoItem);
+            let debug_info_off = self
+                .section_manager
+                .get_aligned_size(Section::DebugInfoItem);
             let item = DebugInfoItem::deserialize_from_slice(&code.debug_info)?;
             self.section_manager
                 .add_elt(Section::DebugInfoItem, Some(item.size()));
@@ -1409,7 +1411,7 @@ impl DexWriter {
                 Uleb128(class.direct_methods.get(id).unwrap().get_raw_access_flags());
             // No if let because ownership gunfooterie
             let code_off = if class.direct_methods.get(id).unwrap().code.is_some() {
-                let code_off = self.section_manager.get_size(Section::CodeItem);
+                let code_off = self.section_manager.get_aligned_size(Section::CodeItem);
                 self.insert_code_item(id.clone(), true)?;
                 Uleb128(code_off + 1)
             } else {
@@ -1444,7 +1446,7 @@ impl DexWriter {
             );
             // No if let because ownership gunfooterie
             let code_off = if class.virtual_methods.get(id).unwrap().code.is_some() {
-                let code_off = self.section_manager.get_size(Section::CodeItem);
+                let code_off = self.section_manager.get_aligned_size(Section::CodeItem);
                 self.insert_code_item(id.clone(), false)?;
                 Uleb128(code_off + 1)
             } else {
@@ -1645,7 +1647,9 @@ impl DexWriter {
         values.push(DexValue::MethodType(call_site.type_.clone()));
         values.extend(call_site.args.iter().cloned());
         self.call_site_ids.push(CallSiteIdItem {
-            call_site_off: self.section_manager.get_size(Section::EncodedArrayItem),
+            call_site_off: self
+                .section_manager
+                .get_aligned_size(Section::EncodedArrayItem),
         }); // linked in link_call_site_ids()
         self.section_manager.add_elt(Section::CallSiteIdItem, None);
         self.insert_encoded_array_item(DexArray(values))
@@ -1722,7 +1726,9 @@ impl DexWriter {
         annotations.sort_by_key(|annot| annot.annotation.type_.clone());
         for annot in annotations {
             annotation_set.entries.push(AnnotationOffItem {
-                annotation_off: self.section_manager.get_size(Section::AnnotationItem),
+                annotation_off: self
+                    .section_manager
+                    .get_aligned_size(Section::AnnotationItem),
             }); // linked in link_annotations()
 
             let item = AnnotationItem {
@@ -1769,7 +1775,9 @@ impl DexWriter {
         annotations.sort_by_key(|annot| annot.annotation.type_.clone());
         for annot in annotations {
             annotation_set.entries.push(AnnotationOffItem {
-                annotation_off: self.section_manager.get_size(Section::AnnotationItem),
+                annotation_off: self
+                    .section_manager
+                    .get_aligned_size(Section::AnnotationItem),
             }); // linked in link_annotations()
 
             let item = AnnotationItem {
@@ -1816,7 +1824,9 @@ impl DexWriter {
         annotations.sort_by_key(|annot| annot.annotation.type_.clone());
         for annot in annotations {
             annotation_set.entries.push(AnnotationOffItem {
-                annotation_off: self.section_manager.get_size(Section::AnnotationItem),
+                annotation_off: self
+                    .section_manager
+                    .get_aligned_size(Section::AnnotationItem),
             }); // linked in link_annotations()
 
             let item = AnnotationItem {
@@ -1864,7 +1874,9 @@ impl DexWriter {
         annotations.sort_by_key(|annot| annot.annotation.type_.clone());
         for annot in annotations {
             annotation_set.entries.push(AnnotationOffItem {
-                annotation_off: self.section_manager.get_size(Section::AnnotationItem),
+                annotation_off: self
+                    .section_manager
+                    .get_aligned_size(Section::AnnotationItem),
             }); // linked in link_annotations()
 
             let item = AnnotationItem {
@@ -1914,7 +1926,9 @@ impl DexWriter {
         for (param_idx, has_annotation) in param_has_annotation.into_iter().enumerate() {
             list.list.push(AnnotationSetRefItem {
                 annotations_off: if has_annotation {
-                    let annotation_off = self.section_manager.get_size(Section::AnnotationSetItem);
+                    let annotation_off = self
+                        .section_manager
+                        .get_aligned_size(Section::AnnotationSetItem);
                     self.insert_parameters_annotation_set(method_id, is_direct_method, param_idx)?;
                     annotation_off + 1
                 } else {
@@ -1942,7 +1956,9 @@ impl DexWriter {
     fn insert_annotations(&mut self, class_id: &IdType) -> Result<()> {
         let (class, _) = self.class_defs.get(class_id).unwrap();
         let class_annotations_off = if !class.annotations.is_empty() {
-            let class_annotations_off = self.section_manager.get_size(Section::AnnotationSetItem);
+            let class_annotations_off = self
+                .section_manager
+                .get_aligned_size(Section::AnnotationSetItem);
             self.insert_class_annotation_set(class_id)
                 .with_context(|| {
                     format!(
@@ -1973,7 +1989,10 @@ impl DexWriter {
                     field_id.__repr__(), class_id.__repr__()),
             };
             if !field.annotations.is_empty() {
-                let annotations_off = self.section_manager.get_size(Section::AnnotationSetItem) + 1;
+                let annotations_off = self
+                    .section_manager
+                    .get_aligned_size(Section::AnnotationSetItem)
+                    + 1;
                 self.insert_field_annotation_set(&field_id, is_static)?;
                 field_annotations.push(FieldAnnotation {
                     field_idx: *self.field_ids.get(&field_id).ok_or(anyhow!(
@@ -2004,7 +2023,10 @@ impl DexWriter {
                     method_id.__repr__(), class_id.__repr__()),
             };
             if !method.annotations.is_empty() {
-                let annotations_off = self.section_manager.get_size(Section::AnnotationSetItem) + 1;
+                let annotations_off = self
+                    .section_manager
+                    .get_aligned_size(Section::AnnotationSetItem)
+                    + 1;
                 self.insert_method_annotation_set(method_id, is_direct)?;
                 method_annotations.push(MethodAnnotation {
                     method_idx: *self.method_ids.get(method_id).ok_or(anyhow!(
@@ -2030,8 +2052,10 @@ impl DexWriter {
                     method_id.__repr__(), class_id.__repr__()),
             };
             if !method.parameters_annotations.is_empty() {
-                let annotations_off =
-                    self.section_manager.get_size(Section::AnnotationSetRefList) + 1;
+                let annotations_off = self
+                    .section_manager
+                    .get_aligned_size(Section::AnnotationSetRefList)
+                    + 1;
                 self.insert_parameters_annotation_set_list(&method_id, is_direct)?;
                 parameter_annotations.push(ParameterAnnotation {
                     method_idx: *self.method_ids.get(&method_id).ok_or(anyhow!(
@@ -2081,7 +2105,9 @@ impl DexWriter {
             .and_modify(|(_, i)| *i = idx);
         let (class, _) = self.class_defs.get(class_id).unwrap();
         let class_data_off = if class.has_data_item() {
-            let class_data_off = self.section_manager.get_size(Section::ClassDataItem);
+            let class_data_off = self
+                .section_manager
+                .get_aligned_size(Section::ClassDataItem);
             self.insert_class_data_item(class_id)?;
             class_data_off + 1
         } else {
@@ -2091,7 +2117,9 @@ impl DexWriter {
         // mutating self with `insert_class_data_item`, and get a new ref afterward
         let (class, _) = self.class_defs.get(class_id).unwrap();
         let static_values_off = if class.has_static_values_array() {
-            let static_values_off = self.section_manager.get_size(Section::EncodedArrayItem);
+            let static_values_off = self
+                .section_manager
+                .get_aligned_size(Section::EncodedArrayItem);
             self.insert_class_static_values(class_id)?;
             static_values_off + 1
         } else {
@@ -2101,7 +2129,7 @@ impl DexWriter {
         let annotations_off = if class.has_annotations() {
             let annotations_off = self
                 .section_manager
-                .get_size(Section::AnnotationsDirectoryItem);
+                .get_aligned_size(Section::AnnotationsDirectoryItem);
             self.insert_annotations(class_id)?;
             annotations_off + 1
         } else {
@@ -2255,7 +2283,7 @@ impl DexWriter {
         self.header.method_ids_off = self.section_manager.get_offset(Section::MethodIdItem);
         self.header.class_defs_size = self.section_manager.get_nb_elt(Section::ClassDefItem) as u32;
         self.header.class_defs_off = self.section_manager.get_offset(Section::ClassDefItem);
-        self.header.data_size = self.section_manager.get_size(Section::Data);
+        self.header.data_size = self.section_manager.get_unaligned_size(Section::Data);
         self.header.data_off = self.section_manager.get_offset(Section::Data);
     }
 
@@ -2622,6 +2650,8 @@ impl DexWriter {
         let mut hasher = Sha1::new();
         io::copy(&mut buffer, &mut hasher)?;
         self.header.signature = hasher.finalize().into();
+        let size = buffer.seek(SeekFrom::End(0))? as u32;
+        self.header.file_size = size;
         buffer.rewind()?;
         self.header.serialize(&mut buffer)?;
 
@@ -3009,7 +3039,7 @@ impl SectionManager {
         size
     }
 
-    fn get_size(&self, section: Section) -> u32 {
+    fn get_unaligned_size(&self, section: Section) -> u32 {
         if section.is_data() {
             self.sizes[section.get_index()..].iter().sum()
         } else {
@@ -3017,6 +3047,15 @@ impl SectionManager {
         }
     }
 
+    /// The position of a potential new item in the section considering alignment.
+    fn get_aligned_size(&self, section: Section) -> u32 {
+        let mut size = self.get_unaligned_size(section);
+        while size % section.get_item_alignment() != 0 {
+            size += 1;
+        }
+        size
+    }
+
     fn get_nb_elt(&self, section: Section) -> usize {
         self.nb_elt[section.get_index()]
     }
@@ -3045,7 +3084,7 @@ impl SectionManager {
     fn show(&self) {
         let mut offset = 0;
         for section in Section::VARIANT_LIST {
-            let size = self.get_size(*section);
+            let size = self.get_unaligned_size(*section);
             let new_offset = offset + size;
             let nb_elt = self.get_nb_elt(*section);
             println!(