diff --git a/libgit2-sys/lib.rs b/libgit2-sys/lib.rs
index a113a29526..691753b26e 100644
--- a/libgit2-sys/lib.rs
+++ b/libgit2-sys/lib.rs
@@ -692,6 +692,7 @@ git_enum! {
         GIT_FILEMODE_UNREADABLE = 0o000000,
         GIT_FILEMODE_TREE = 0o040000,
         GIT_FILEMODE_BLOB = 0o100644,
+        GIT_FILEMODE_BLOB_GROUP_WRITABLE = 0o100664,
         GIT_FILEMODE_BLOB_EXECUTABLE = 0o100755,
         GIT_FILEMODE_LINK = 0o120000,
         GIT_FILEMODE_COMMIT = 0o160000,
diff --git a/src/diff.rs b/src/diff.rs
index 3d5b42d9dc..de1481d565 100644
--- a/src/diff.rs
+++ b/src/diff.rs
@@ -621,6 +621,7 @@ impl<'a> DiffFile<'a> {
             raw::GIT_FILEMODE_UNREADABLE => FileMode::Unreadable,
             raw::GIT_FILEMODE_TREE => FileMode::Tree,
             raw::GIT_FILEMODE_BLOB => FileMode::Blob,
+            raw::GIT_FILEMODE_BLOB_GROUP_WRITABLE => FileMode::BlobGroupWritable,
             raw::GIT_FILEMODE_BLOB_EXECUTABLE => FileMode::BlobExecutable,
             raw::GIT_FILEMODE_LINK => FileMode::Link,
             raw::GIT_FILEMODE_COMMIT => FileMode::Commit,
diff --git a/src/lib.rs b/src/lib.rs
index c297ffe444..df25092a9b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1098,6 +1098,8 @@ pub enum FileMode {
     Tree,
     /// Blob
     Blob,
+    /// Group writable blob. Obsolete mode kept for compatibility reasons
+    BlobGroupWritable,
     /// Blob executable
     BlobExecutable,
     /// Link
@@ -1112,6 +1114,7 @@ impl From<FileMode> for i32 {
             FileMode::Unreadable => raw::GIT_FILEMODE_UNREADABLE as i32,
             FileMode::Tree => raw::GIT_FILEMODE_TREE as i32,
             FileMode::Blob => raw::GIT_FILEMODE_BLOB as i32,
+            FileMode::BlobGroupWritable => raw::GIT_FILEMODE_BLOB_GROUP_WRITABLE as i32,
             FileMode::BlobExecutable => raw::GIT_FILEMODE_BLOB_EXECUTABLE as i32,
             FileMode::Link => raw::GIT_FILEMODE_LINK as i32,
             FileMode::Commit => raw::GIT_FILEMODE_COMMIT as i32,
@@ -1125,6 +1128,7 @@ impl From<FileMode> for u32 {
             FileMode::Unreadable => raw::GIT_FILEMODE_UNREADABLE as u32,
             FileMode::Tree => raw::GIT_FILEMODE_TREE as u32,
             FileMode::Blob => raw::GIT_FILEMODE_BLOB as u32,
+            FileMode::BlobGroupWritable => raw::GIT_FILEMODE_BLOB_GROUP_WRITABLE as u32,
             FileMode::BlobExecutable => raw::GIT_FILEMODE_BLOB_EXECUTABLE as u32,
             FileMode::Link => raw::GIT_FILEMODE_LINK as u32,
             FileMode::Commit => raw::GIT_FILEMODE_COMMIT as u32,
@@ -1562,8 +1566,10 @@ mod tests {
     #[test]
     fn convert_filemode() {
         assert_eq!(i32::from(FileMode::Blob), 0o100644);
+        assert_eq!(i32::from(FileMode::BlobGroupWritable), 0o100664);
         assert_eq!(i32::from(FileMode::BlobExecutable), 0o100755);
         assert_eq!(u32::from(FileMode::Blob), 0o100644);
+        assert_eq!(u32::from(FileMode::BlobGroupWritable), 0o100664);
         assert_eq!(u32::from(FileMode::BlobExecutable), 0o100755);
     }
 }
diff --git a/systest/build.rs b/systest/build.rs
index eba93f3090..f0533cde25 100644
--- a/systest/build.rs
+++ b/systest/build.rs
@@ -39,6 +39,9 @@ fn main() {
         }
     });
 
+    // GIT_FILEMODE_BLOB_GROUP_WRITABLE is not a public const in libgit2
+    cfg.define("GIT_FILEMODE_BLOB_GROUP_WRITABLE", Some("0100664"));
+
     // not entirely sure why this is failing...
     cfg.skip_roundtrip(|t| t == "git_clone_options" || t == "git_submodule_update_options");