diff --git a/src/cdtools/tools/data/data.py b/src/cdtools/tools/data/data.py
index 19e7467..ed13542 100644
--- a/src/cdtools/tools/data/data.py
+++ b/src/cdtools/tools/data/data.py
@@ -485,9 +485,9 @@ def add_entry_info(cxi_file, metadata):
     # included in case the cxi spec becomes more permissive
     for key, value in metadata.items():
         if isinstance(value,(str,bytes)):
-            cxi_file['entry_1'][key] = np.string_(value)
+            cxi_file['entry_1'][key] = np.bytes_(value)
         elif isinstance(value, datetime.datetime):
-            cxi_file['entry_1'][key] = np.string_(value.isoformat())
+            cxi_file['entry_1'][key] = np.bytes_(value.isoformat())
         elif isinstance(value, numbers.Number):
             cxi_file['entry_1'][key] = value
         elif isinstance(value, (np.ndarray,list,tuple)):
@@ -525,9 +525,9 @@ def add_sample_info(cxi_file, metadata):
         if key == 'orientation':
             continue # this is a special case
         if isinstance(value,(str,bytes)):
-            s1[key] = np.string_(value)
+            s1[key] = np.bytes_(value)
         elif isinstance(value, datetime.datetime):
-            s1[key] = np.string_(value.isoformat())
+            s1[key] = np.bytes_(value.isoformat())
         elif isinstance(value, numbers.Number):
             s1[key] = value
         elif isinstance(value, (np.ndarray,list,tuple)):
@@ -701,7 +701,7 @@ def add_data(cxi_file, data, axes=None, compression='gzip',
             axes_str = ':'.join(axes)
         else:
             axes_str = str(axes)
-        det1['data'].attrs['axes'] = np.string_(axes_str)
+        det1['data'].attrs['axes'] = np.bytes_(axes_str)
 
         
 def add_shot_to_shot_info(cxi_file, data, field_name):
diff --git a/tests/conftest.py b/tests/conftest.py
index 9eceb0c..ca3a2c7 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -77,28 +77,28 @@ def ptycho_cxi_1():
     expected['entry metadata'] = {}
     e1e = expected['entry metadata']
     e1e['start_time'] = datetime.datetime.now()
-    e1f['start_time'] = np.string_(e1e['start_time'].isoformat())
+    e1f['start_time'] = np.bytes_(e1e['start_time'].isoformat())
     e1e['end_time'] = datetime.datetime.now()
-    e1f['end_time'] = np.string_(e1e['end_time'].isoformat())
+    e1f['end_time'] = np.bytes_(e1e['end_time'].isoformat())
     e1e['experiment_identifier'] = 'Fake Experiment 1'
-    e1f['experiment_identifier'] = np.string_(e1e['experiment_identifier'])
+    e1f['experiment_identifier'] = np.bytes_(e1e['experiment_identifier'])
     e1e['experiment_description'] = 'A fully defined ptychography experiment to test the data loading'
-    e1f['experiment_description'] = np.string_(e1e['experiment_description'])
+    e1f['experiment_description'] = np.bytes_(e1e['experiment_description'])
     e1e['program_name'] = 'cdtools'
-    e1f['program_name'] = np.string_(e1e['program_name'])
+    e1f['program_name'] = np.bytes_(e1e['program_name'])
     e1e['title'] = 'The one experiment we did'
-    e1f['title'] = np.string_(e1e['title'])
+    e1f['title'] = np.bytes_(e1e['title'])
 
     # Set up the sample info
     s1f = e1f.create_group('sample_1')
     expected['sample info'] = {}
     s1e = expected['sample info']
     s1e['name'] = 'Fake Sample'
-    s1f['name'] = np.string_(s1e['name'])
+    s1f['name'] = np.bytes_(s1e['name'])
     s1e['description'] = 'A sample that isn\'t real'
-    s1f['description'] = np.string_(s1e['description'])
+    s1f['description'] = np.bytes_(s1e['description'])
     s1e['unit_cell_group'] = 'P1'
-    s1f['unit_cell_group'] = np.string_(s1e['unit_cell_group'])
+    s1f['unit_cell_group'] = np.bytes_(s1e['unit_cell_group'])
     s1e['concentration'] = np.float32(np.random.rand())
     s1f['concentration'] = s1e['concentration']
     s1e['mass'] = np.float32(np.random.rand())
@@ -151,7 +151,7 @@ def ptycho_cxi_1():
     d1f.create_dataset('data',data=data)
     data1f['data'] = h5py.SoftLink('/entry_1/instrument_1/detector_1/data')
 
-    d1f['data'].attrs['axes'] = np.string_('translation:y:x')
+    d1f['data'].attrs['axes'] = np.bytes_('translation:y:x')
     expected['axes'] = ['translation','y','x']
 
     g1f = s1f.create_group('geometry_1')
@@ -196,7 +196,7 @@ def ptycho_cxi_2():
     expected['entry metadata'] = {}
     e1e = expected['entry metadata']
     e1e['title'] = 'The one experiment we did'
-    e1f['title'] = np.string_(e1e['title'])
+    e1f['title'] = np.bytes_(e1e['title'])
 
     # Set up the sample info
     s1f = e1f.create_group('sample_1')
@@ -277,9 +277,9 @@ def ptycho_cxi_3():
     expected['entry metadata'] = {}
     e1e = expected['entry metadata']
     e1e['start_time'] = datetime.datetime.now()
-    e1f['start_time'] = np.string_(e1e['start_time'].isoformat())
+    e1f['start_time'] = np.bytes_(e1e['start_time'].isoformat())
     e1e['end_time'] = datetime.datetime.now()
-    e1f['end_time'] = np.string_(e1e['end_time'].isoformat())
+    e1f['end_time'] = np.bytes_(e1e['end_time'].isoformat())
 
     # Set up the sample info
     expected['sample info'] = None
@@ -314,7 +314,7 @@ def ptycho_cxi_3():
     expected['data'] = data
     data1f.create_dataset('data',data=data)
 
-    data1f['data'].attrs['axes'] = np.string_('translation:y:x')
+    data1f['data'].attrs['axes'] = np.bytes_('translation:y:x')
     expected['axes'] = ['translation','y','x']
 
     translations = np.arange(300).reshape((100,3)).astype(np.float32)