diff --git a/gext/main.py b/gext/main.py
index b48594a0962b3360d8a7b3c2725ea7d6bd504833..76af6a80b510b9f702b7290a71bc3526ae7473aa 100644
--- a/gext/main.py
+++ b/gext/main.py
@@ -22,6 +22,7 @@ class Extrapolator:
             "descriptor": "distance",
             "fitting": "leastsquare",
             "allow_partially_filled": True,
+            "store_overlap": True,
         }
 
         self.nelectrons = nelectrons
@@ -30,9 +31,10 @@ class Extrapolator:
         self.set_options(**kwargs)
 
         self.gammas = CircularBuffer(self.options["nsteps"], (self.nelectrons//2, self.nbasis))
-        self.overlaps = CircularBuffer(self.options["nsteps"], (self.nbasis, self.nbasis))
         self.descriptors = CircularBuffer(self.options["nsteps"],
             ((self.natoms - 1)*self.natoms//2, ))
+        if self.options["store_overlap"]:
+            self.overlaps = CircularBuffer(self.options["nsteps"], (self.nbasis, self.nbasis))
 
         self.tangent: Optional[np.ndarray] = None
 
@@ -78,8 +80,7 @@ class Extrapolator:
             raise ValueError("Unsupported descriptor")
         self.fitting_calculator.set_options(**fitting_options)
 
-    def load_data(self, coords: np.ndarray, coeff: np.ndarray,
-            overlap: np.ndarray):
+    def load_data(self, coords: np.ndarray, coeff: np.ndarray, overlap):
         """Load a new data point in the extrapolator."""
 
         # Crop the coefficient matrix up to the number of electron
@@ -94,14 +95,16 @@ class Extrapolator:
         # push the new data to the corresponding vectors
         self.gammas.push(self._grassmann_log(coeff))
         self.descriptors.push(self._compute_descriptor(coords))
-        self.overlaps.push(overlap)
 
-    def guess(self, coords: np.ndarray, overlap = None) -> np.ndarray:
+        if self.options["store_overlap"]:
+            self.overlaps.push(overlap)
+
+    def guess(self, coords: np.ndarray, overlap=None) -> np.ndarray:
         """Get a new electronic density matrix to be used as a guess."""
         c_guess = self.guess_coefficients(coords, overlap)
         return c_guess @ c_guess.T
 
-    def guess_coefficients(self, coords: np.ndarray, overlap = None) -> np.ndarray:
+    def guess_coefficients(self, coords: np.ndarray, overlap=None) -> np.ndarray:
         """Get a new coefficient matrix to be used as a guess."""
 
         # check if we have enough data points to perform an extrapolation
@@ -115,6 +118,9 @@ class Extrapolator:
             if count < n:
                 raise ValueError("Not enough data loaded in the extrapolator")
 
+        if overlap is None and not self.options["store_overlap"]:
+            raise ValueError("Guessing without overlap requires `store_overlap` true.")
+
         # use the descriptors to find the fitting coefficients
         prev_descriptors = self.descriptors.get(n)
         descriptor = self._compute_descriptor(coords)