diff --git a/src/waveresponse/_core.py b/src/waveresponse/_core.py
index d11839e..0ed1588 100644
--- a/src/waveresponse/_core.py
+++ b/src/waveresponse/_core.py
@@ -2149,6 +2149,9 @@ def dirm(self, degrees=None):
             during instantiation.
         """
 
+        if degrees is None:
+            degrees = self._degrees
+
         dp, sp = self.spectrum1d(axis=0, degrees=False)
 
         d = self._full_range_dir(dp)