diff --git a/ismrmrd/image.py b/ismrmrd/image.py
index 2b2044b..b4ecb27 100644
--- a/ismrmrd/image.py
+++ b/ismrmrd/image.py
@@ -44,6 +44,7 @@ def get_data_type_from_dtype(dtype):
 # Image Header
 class ImageHeader(FlagsMixin, EqualityMixin, ctypes.Structure):
     _pack_ = 2
+    _layout_ = 'ms'
     _fields_ = [("version", ctypes.c_uint16),
                 ("data_type", ctypes.c_uint16),
                 ("flags", ctypes.c_uint64),
diff --git a/ismrmrd/waveform.py b/ismrmrd/waveform.py
index 239a0c4..8ca5de3 100644
--- a/ismrmrd/waveform.py
+++ b/ismrmrd/waveform.py
@@ -9,6 +9,7 @@
 
 class WaveformHeader(FlagsMixin, EqualityMixin, ctypes.Structure):
     _pack_ = 8
+    _layout_ = 'ms'
     _fields_ = [("version", ctypes.c_uint16),
                 ("flags", ctypes.c_uint64),
                 ("measurement_uid", ctypes.c_uint32),