diff --git a/qupulse/program/waveforms.py b/qupulse/program/waveforms.py
index 9cdcbf4f..e08e410f 100644
--- a/qupulse/program/waveforms.py
+++ b/qupulse/program/waveforms.py
@@ -369,8 +369,8 @@ def unsafe_sample(self,
             entries = self._table
 
         for entry1, entry2 in pairwise(entries):
-            indices = slice(np.searchsorted(sample_times, entry1.t, 'left'),
-                            np.searchsorted(sample_times, entry2.t, 'right'))
+            indices = slice(sample_times.searchsorted(entry1.t, 'left'),
+                            sample_times.searchsorted(entry2.t, 'right'))
             output_array[indices] = \
                 entry2.interp((float(entry1.t), entry1.v),
                               (float(entry2.t), entry2.v),
@@ -626,7 +626,7 @@ def unsafe_sample(self,
             # indexing in numpy and their copy/reference behaviour
             end = time + subwaveform.duration
 
-            indices = slice(*np.searchsorted(sample_times, (float(time), float(end)), 'left'))
+            indices = slice(*sample_times.searchsorted((float(time), float(end)), 'left'))
             subwaveform.unsafe_sample(channel=channel,
                                       sample_times=sample_times[indices]-np.float64(time),
                                       output_array=output_array[indices])
@@ -843,7 +843,7 @@ def unsafe_sample(self,
         time = 0
         for _ in range(self._repetition_count):
             end = time + body_duration
-            indices = slice(*np.searchsorted(sample_times, (float(time), float(end)), 'left'))
+            indices = slice(*sample_times.searchsorted((float(time), float(end)), 'left'))
             self._body.unsafe_sample(channel=channel,
                                      sample_times=sample_times[indices] - float(time),
                                      output_array=output_array[indices])