diff --git a/ismrmrd/acquisition.py b/ismrmrd/acquisition.py
index bbf9df6..c2baca9 100644
--- a/ismrmrd/acquisition.py
+++ b/ismrmrd/acquisition.py
@@ -11,6 +11,7 @@
 
 class EncodingCounters(EqualityMixin, ctypes.Structure):
     _pack_ = 2
+    _layout_ = "ms"
     _fields_ = [("kspace_encode_step_1", ctypes.c_uint16),
                 ("kspace_encode_step_2", ctypes.c_uint16),
                 ("average", ctypes.c_uint16),
@@ -35,6 +36,7 @@ def __str__(self):
 
 class AcquisitionHeader(FlagsMixin, ChannelMaskMixin, EqualityMixin, ctypes.Structure):
     _pack_ = 2
+    _layout_ = "ms"
     _fields_ = [("version", ctypes.c_uint16),
                 ("flags", ctypes.c_uint64),
                 ("measurement_uid", ctypes.c_uint32),
diff --git a/ismrmrd/image.py b/ismrmrd/image.py
index 2b2044b..05721b2 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..74e8c5a 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),