diff --git a/src/compress/mod.rs b/src/compress/mod.rs
index 110221e..9b8cec4 100644
--- a/src/compress/mod.rs
+++ b/src/compress/mod.rs
@@ -649,12 +649,13 @@ impl Compressor {
 
         if in_idx == 0 && flush_mode == FlushMode::Finish {
             let start_out = bs.out_idx;
+            let start_bitcount = bs.bitcount;
             if self.compression_level >= 10 {
                 self.compress_near_optimal_block(mf, input, 0, bs, true);
             } else {
                 self.compress_greedy_block(mf, input, 0, bs, 0, true);
             }
-            if bs.out_idx == start_out {
+            if bs.out_idx == start_out && bs.bitcount == start_bitcount {
                 mf.advance(input.len());
                 return (CompressResult::InsufficientSpace, 0, 0);
             }
diff --git a/tests/buffer_size_test.rs b/tests/buffer_size_test.rs
new file mode 100644
index 0000000..82a2c23
--- /dev/null
+++ b/tests/buffer_size_test.rs
@@ -0,0 +1,67 @@
+use libdeflate::stream::DeflateEncoder;
+use std::io::Write;
+use std::sync::{Arc, Mutex};
+
+#[derive(Clone)]
+struct SharedWriter {
+    data: Arc<Mutex<Vec<u8>>>,
+}
+
+impl Write for SharedWriter {
+    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
+        let mut data = self.data.lock().unwrap();
+        data.extend_from_slice(buf);
+        Ok(buf.len())
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        Ok(())
+    }
+}
+
+#[test]
+fn test_with_buffer_size() {
+    let writer_data = Arc::new(Mutex::new(Vec::new()));
+    let writer = SharedWriter {
+        data: writer_data.clone(),
+    };
+
+    let buffer_size = 100;
+    // Buffer size 100, we write 150 bytes.
+    let mut encoder = DeflateEncoder::new(writer, 1).with_buffer_size(buffer_size);
+
+    let data = vec![0u8; 150];
+    encoder.write_all(&data).unwrap();
+
+    // The buffer size (100) is exceeded by 150 bytes, so flush_buffer(false) should be called.
+    // flush_buffer compresses and writes to the underlying writer.
+    let compressed_len = writer_data.lock().unwrap().len();
+    assert!(compressed_len > 0, "Encoder should have flushed when buffer limit was exceeded");
+
+    // Finish the stream
+    encoder.finish().unwrap();
+
+    let final_len = writer_data.lock().unwrap().len();
+    assert!(final_len > compressed_len, "Finish should write more data (footer/final block)");
+}
+
+#[test]
+fn test_default_buffer_size() {
+    let writer_data = Arc::new(Mutex::new(Vec::new()));
+    let writer = SharedWriter {
+        data: writer_data.clone(),
+    };
+
+    // Default buffer size is usually large (e.g. 1MB).
+    let mut encoder = DeflateEncoder::new(writer, 1);
+
+    let data = vec![0u8; 150];
+    encoder.write_all(&data).unwrap();
+
+    // Should not have flushed yet as 150 < default buffer size
+    let compressed_len = writer_data.lock().unwrap().len();
+    assert_eq!(compressed_len, 0, "Encoder should NOT have flushed with default buffer size");
+
+    encoder.finish().unwrap();
+    assert!(writer_data.lock().unwrap().len() > 0);
+}