diff --git a/grext/main.py b/grext/main.py
index 7249619887fff8ac1846b22fa17860ffcc181488..c9aeb9d0ea04496d83fe6079990508f906e50b15 100644
--- a/grext/main.py
+++ b/grext/main.py
@@ -46,7 +46,7 @@ class Extrapolator:
         self.descriptors.push(self._compute_descriptor(coords))
         self.overlaps.push(overlap)
 
-    def guess(self, coords: np.ndarray, overlap: Optional[np.ndarray] = None) -> np.ndarray:
+    def guess(self, coords: np.ndarray, overlap = None) -> np.ndarray:
         """Get a new electronic density to be used as a guess."""
 
         prev_descriptors = self.descriptors.get(self.nsteps)