diff --git a/src/internal/directory.rs b/src/internal/directory.rs
index 8e22da9..a44f6ba 100644
--- a/src/internal/directory.rs
+++ b/src/internal/directory.rs
@@ -413,6 +413,7 @@ impl<F: Write + Seek> Directory<F> {
         if self.dir_entries.len() % dir_entries_per_sector == 0 {
             let start_sector = self.dir_start_sector;
             self.allocator.extend_chain(start_sector, SectorInit::Dir)?;
+            self.update_num_dir_sectors()?;
         }
         // Add a new entry to the end of the directory and return it.
         let stream_id = self.dir_entries.len() as u32;
@@ -420,6 +421,27 @@ impl<F: Write + Seek> Directory<F> {
         Ok(stream_id)
     }
 
+    /// Increase header num_dir_sectors if version V4
+    /// note: not updating this value breaks ole32 compatibility
+    fn update_num_dir_sectors(&mut self) -> io::Result<()> {
+        let start_sector = self.dir_start_sector;
+        if self.version() == Version::V4 {
+            let num_dir_sectors = self.count_directory_sectors(start_sector)?;
+            self.seek_within_header(40)?.write_u32::<LittleEndian>(num_dir_sectors)?;
+        }
+        Ok(())
+    }
+
+    fn count_directory_sectors(&mut self, start_sector: u32) -> io::Result<u32> {
+        let mut num_dir_sectors = 1;
+        let mut next_sector = self.allocator.next(start_sector)?;
+        while next_sector != consts::END_OF_CHAIN {
+            num_dir_sectors += 1;
+            next_sector = self.allocator.next(next_sector)?;
+        }
+        Ok(num_dir_sectors)
+    }
+
     /// Deallocates the specified directory entry.
     fn free_dir_entry(&mut self, stream_id: u32) -> io::Result<()> {
         debug_assert_ne!(stream_id, consts::ROOT_STREAM_ID);
@@ -428,6 +450,7 @@ impl<F: Write + Seek> Directory<F> {
         *self.dir_entry_mut(stream_id) = dir_entry;
         // TODO: Truncate directory chain if last directory sector is now all
         //       unallocated.
+        //       In that case, also call update_num_dir_sectors()
         Ok(())
     }
 
diff --git a/src/lib.rs b/src/lib.rs
index 96c146f..73f845b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -493,7 +493,15 @@ impl<F: Read + Seek> CompoundFile<F> {
         let mut dir_entries = Vec::<DirEntry>::new();
         let mut seen_dir_sectors = FnvHashSet::default();
         let mut current_dir_sector = header.first_dir_sector;
+        let mut dir_sector_count = 1;
         while current_dir_sector != consts::END_OF_CHAIN {
+            if validation.is_strict() && header.version == Version::V4 && dir_sector_count > header.num_dir_sectors {
+                invalid_data!(
+                    "Directory chain includes at least {} sectors which is greater than header num_dir_sectors {}",
+                    dir_sector_count,
+                    header.num_dir_sectors
+                );
+            }
             if current_dir_sector > consts::MAX_REGULAR_SECTOR {
                 invalid_data!(
                     "Directory chain includes invalid sector index {}",
@@ -526,6 +534,7 @@ impl<F: Read + Seek> CompoundFile<F> {
                 }
             }
             current_dir_sector = allocator.next(current_dir_sector)?;
+            dir_sector_count += 1;
         }
 
         let mut directory = Directory::new(
diff --git a/tests/malformed.rs b/tests/malformed.rs
index 5971954..4057593 100644
--- a/tests/malformed.rs
+++ b/tests/malformed.rs
@@ -456,3 +456,29 @@ fn open_difat_terminate_freesect() {
 fn open_strict_difat_terminate_freesect() {
     CompoundFile::open_strict(difat_terminate_in_freesect()).unwrap();
 }
+
+/// Regression test for https://github.com/mdsteele/rust-cfb/issues/52.
+#[test]
+#[should_panic(
+expected = "Directory chain includes at least 2 sectors which is greater than header num_dir_sectors 1"
+)]
+fn invalid_num_dir_sectors_issue_52() {
+    // Create a CFB file with 2 sectors for the directory.
+    let cursor = Cursor::new(Vec::new());
+    let mut comp = CompoundFile::create(cursor).unwrap();
+    for i in 0..32 {
+        let path = format!("stream{}", i);
+        let path = Path::new(&path);
+        comp.create_stream(path).unwrap();
+    }
+    comp.flush().unwrap();
+
+    // update the header to contain have num_dir_sectors = 1
+    let mut cursor = comp.into_inner();
+    cursor.seek(SeekFrom::Start(40)).unwrap();
+    cursor.write_all(&[0x01, 0x00, 0x00, 0x00]).unwrap();
+    cursor.flush().unwrap();
+
+    // Read the file back in.
+    CompoundFile::open_strict(cursor).unwrap();
+}