diff --git a/qcodes_contrib_drivers/drivers/Keysight/SD_common/SD_AWG_Async.py b/qcodes_contrib_drivers/drivers/Keysight/SD_common/SD_AWG_Async.py
index 59d005346..0cdac4fc1 100644
--- a/qcodes_contrib_drivers/drivers/Keysight/SD_common/SD_AWG_Async.py
+++ b/qcodes_contrib_drivers/drivers/Keysight/SD_common/SD_AWG_Async.py
@@ -445,15 +445,16 @@ def _init_awg_memory(self):
         self.log.info(f'Reserving awg memory for {len(new_slots)} slots')
 
         zeros = []
+        wave = None
         total_size = 0
         total_duration = 0
         for slot in new_slots:
             start = time.perf_counter()
-            if len(zeros) != slot.size:
+            if len(zeros) != slot.size or wave is None:
                 zeros = np.zeros(slot.size, np.float)
                 wave = keysightSD1.SD_Wave()
                 result_parser(wave.newFromArrayDouble(keysightSD1.SD_WaveformTypes.WAVE_ANALOG, zeros))
-                super().load_waveform(wave, slot.number)
+            super().load_waveform(wave, slot.number)
             duration = time.perf_counter() - start
             total_duration += duration
             total_size += slot.size