diff --git a/src/qibolab/instruments/qm/config.py b/src/qibolab/instruments/qm/config.py
index d8626ec9a..bc5f8d663 100644
--- a/src/qibolab/instruments/qm/config.py
+++ b/src/qibolab/instruments/qm/config.py
@@ -313,12 +313,12 @@ def register_waveform(self, pulse, mode="i"):
             serial (str): String with a serialization of the waveform.
                 Used as key to identify the waveform in the config.
         """
-        # Maybe need to force zero q waveforms
-        # if pulse.type.name == "READOUT" and mode == "q":
-        #    serial = "zero_wf"
-        #    if serial not in self.waveforms:
-        #        self.waveforms[serial] = {"type": "constant", "sample": 0.0}
-        if isinstance(pulse.shape, Rectangular):
+        if pulse.type is PulseType.READOUT and mode == "q":
+            # Force zero q waveforms for readout
+            serial = "zero_wf"
+            if serial not in self.waveforms:
+                self.waveforms[serial] = {"type": "constant", "sample": 0.0}
+        elif isinstance(pulse.shape, Rectangular):
             serial = f"constant_wf{pulse.amplitude}"
             if serial not in self.waveforms:
                 self.waveforms[serial] = {"type": "constant", "sample": pulse.amplitude}