diff --git a/CHANGELOG.md b/CHANGELOG.md
index 27afb35cc3..7604ef8a04 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 - switch deprecated transitive dependency `net2`->`socket2` [in `crossterm`->`mio`] ([#66](https://github.com/extrawurst/gitui/issues/66))
 - crash diffing stash created on command line ([#178](https://github.com/extrawurst/gitui/issues/178))
+- delta file size diff on untracked binary files ([#171](https://github.com/extrawurst/gitui/issues/171))
 
 ## [0.8.0] - 2020-07-06
 
diff --git a/asyncgit/src/sync/diff.rs b/asyncgit/src/sync/diff.rs
index 8965b750d3..75c75af23d 100644
--- a/asyncgit/src/sync/diff.rs
+++ b/asyncgit/src/sync/diff.rs
@@ -239,7 +239,7 @@ fn raw_diff_to_file_diff<'a>(
                     let mut patch = Patch::from_buffers(
                         &[],
                         None,
-                        newfile_content.as_bytes(),
+                        newfile_content.as_slice(),
                         Some(&newfile_path),
                         None,
                     )?;
@@ -283,14 +283,16 @@ fn raw_diff_to_file_diff<'a>(
     Ok(res.into_inner())
 }
 
-fn new_file_content(path: &Path) -> Option<String> {
+fn new_file_content(path: &Path) -> Option<Vec<u8>> {
     if let Ok(meta) = fs::symlink_metadata(path) {
         if meta.file_type().is_symlink() {
             if let Ok(path) = fs::read_link(path) {
-                return Some(path.to_str()?.to_string());
+                return Some(
+                    path.to_str()?.to_string().as_bytes().into(),
+                );
             }
         } else if meta.file_type().is_file() {
-            if let Ok(content) = fs::read_to_string(path) {
+            if let Ok(content) = fs::read(path) {
                 return Some(content);
             }
         }
@@ -460,14 +462,20 @@ mod tests {
     }
 
     #[test]
-    fn test_diff_new_binary_file_using_invalid_utf8() -> Result<()> {
+    fn test_diff_delta_size() -> Result<()> {
         let file_path = Path::new("bar");
         let (_td, repo) = repo_init_empty().unwrap();
         let root = repo.path().parent().unwrap();
         let repo_path = root.as_os_str().to_str().unwrap();
 
+        File::create(&root.join(file_path))?.write_all(b"\x00")?;
+
+        stage_add_file(repo_path, file_path).unwrap();
+
+        commit(repo_path, "commit").unwrap();
+
         File::create(&root.join(file_path))?
-            .write_all(b"\xc3\x28")?;
+            .write_all(b"\x00\x02")?;
 
         let diff = get_diff(
             repo_path,
@@ -476,26 +484,22 @@ mod tests {
         )
         .unwrap();
 
-        assert_eq!(diff.hunks.len(), 0);
+        dbg!(&diff);
+        assert_eq!(diff.sizes, (1, 2));
+        assert_eq!(diff.size_delta, 1);
 
         Ok(())
     }
 
     #[test]
-    fn test_diff_delta_size() -> Result<()> {
+    fn test_binary_diff_delta_size_untracked() -> Result<()> {
         let file_path = Path::new("bar");
         let (_td, repo) = repo_init_empty().unwrap();
         let root = repo.path().parent().unwrap();
         let repo_path = root.as_os_str().to_str().unwrap();
 
-        File::create(&root.join(file_path))?.write_all(b"\x00")?;
-
-        stage_add_file(repo_path, file_path).unwrap();
-
-        commit(repo_path, "commit").unwrap();
-
         File::create(&root.join(file_path))?
-            .write_all(b"\x00\x02")?;
+            .write_all(b"\x00\xc7")?;
 
         let diff = get_diff(
             repo_path,
@@ -505,8 +509,8 @@ mod tests {
         .unwrap();
 
         dbg!(&diff);
-        assert_eq!(diff.sizes, (1, 2));
-        assert_eq!(diff.size_delta, 1);
+        assert_eq!(diff.sizes, (0, 2));
+        assert_eq!(diff.size_delta, 2);
 
         Ok(())
     }