diff --git a/src/spikeinterface/core/recording_tools.py b/src/spikeinterface/core/recording_tools.py
index 4b4e1eb3cd..dfba7d1f22 100644
--- a/src/spikeinterface/core/recording_tools.py
+++ b/src/spikeinterface/core/recording_tools.py
@@ -61,7 +61,7 @@ def _init_binary_worker(recording, file_path_dict, dtype, byte_offest):
     worker_ctx["byte_offset"] = byte_offest
     worker_ctx["dtype"] = np.dtype(dtype)
 
-    file_dict = {segment_index: open(file_path, "r+") for segment_index, file_path in file_path_dict.items()}
+    file_dict = {segment_index: open(file_path, "rb+") for segment_index, file_path in file_path_dict.items()}
     worker_ctx["file_dict"] = file_dict
 
     return worker_ctx
@@ -151,34 +151,16 @@ def _write_binary_chunk(segment_index, start_frame, end_frame, worker_ctx):
     num_channels = recording.get_num_channels()
     dtype_size_bytes = np.dtype(dtype).itemsize
 
-    # Calculate byte offsets for the start and end frames relative to the entire recording
+    # Calculate byte offsets for the start frames relative to the entire recording
     start_byte = byte_offset + start_frame * num_channels * dtype_size_bytes
-    end_byte = byte_offset + end_frame * num_channels * dtype_size_bytes
 
-    # The mmap offset must be a multiple of mmap.ALLOCATIONGRANULARITY
-    memmap_offset, start_offset = divmod(start_byte, mmap.ALLOCATIONGRANULARITY)
-    memmap_offset *= mmap.ALLOCATIONGRANULARITY
-
-    # This maps in bytes the region of the memmap that corresponds to the chunk
-    length = (end_byte - start_byte) + start_offset
-    memmap_obj = mmap.mmap(file.fileno(), length=length, access=mmap.ACCESS_WRITE, offset=memmap_offset)
-
-    # To use numpy semantics we use the array interface of the memmap object
-    num_frames = end_frame - start_frame
-    shape = (num_frames, num_channels)
-    memmap_array = np.ndarray(shape=shape, dtype=dtype, buffer=memmap_obj, offset=start_offset)
-
-    # Extract the traces and store them in the memmap array
     traces = recording.get_traces(start_frame=start_frame, end_frame=end_frame, segment_index=segment_index)
-
-    if traces.dtype != dtype:
-        traces = traces.astype(dtype, copy=False)
-
-    memmap_array[...] = traces
-
-    memmap_obj.flush()
-
-    memmap_obj.close()
+    traces = traces.astype(dtype, order="c", copy=False)
+    
+    file.seek(start_byte)
+    file.write(traces.data)
+    # flush is important!!
+    file.flush()
 
 
 write_binary_recording.__doc__ = write_binary_recording.__doc__.format(_shared_job_kwargs_doc)
diff --git a/src/spikeinterface/core/tests/test_baserecording.py b/src/spikeinterface/core/tests/test_baserecording.py
index fc01122269..cdd5897675 100644
--- a/src/spikeinterface/core/tests/test_baserecording.py
+++ b/src/spikeinterface/core/tests/test_baserecording.py
@@ -26,11 +26,14 @@ def test_BaseRecording(create_cache_folder):
     num_samples = 30
     sampling_frequency = 10000
     dtype = "int16"
+    seed = None
+    rng = np.random.default_rng(seed=seed)
 
     file_paths = [cache_folder / f"test_base_recording_{i}.raw" for i in range(num_seg)]
     for i in range(num_seg):
         a = np.memmap(file_paths[i], dtype=dtype, mode="w+", shape=(num_samples, num_chan))
-        a[:] = np.random.randn(*a.shape).astype(dtype)
+        a[:] = rng.normal(scale=5000, size=a.shape).astype(dtype)
+
     rec = BinaryRecordingExtractor(
         file_paths=file_paths, sampling_frequency=sampling_frequency, num_channels=num_chan, dtype=dtype
     )
@@ -201,6 +204,7 @@ def test_BaseRecording(create_cache_folder):
     positions2 = rec_p.get_channel_locations()
     assert np.array_equal(positions2, [[0, 30.0], [0.0, 0.0]])
     traces2 = rec2.get_traces(segment_index=0)
+
     assert np.array_equal(traces2, rec_p.get_traces(segment_index=0))
 
     # from probeinterface.plotting import plot_probe_group, plot_probe
@@ -468,5 +472,8 @@ def test_time_slice_with_time_vector():
 
 
 if __name__ == "__main__":
-    # test_BaseRecording()
-    test_interleaved_probegroups()
+    import tempfile
+    tmp_path = Path(tempfile.mkdtemp())
+
+    test_BaseRecording(tmp_path)
+    # test_interleaved_probegroups()