diff --git a/pyerrors/correlators.py b/pyerrors/correlators.py
index cc3afa4b..94dd2f09 100644
--- a/pyerrors/correlators.py
+++ b/pyerrors/correlators.py
@@ -628,7 +628,7 @@ class Corr:
         function : obj
             function to fit to the data. See fits.least_squares for details.
         fitrange : list
-            Range in which the function is to be fitted to the data.
+            Two element list containing the timeslices on which the fit is supposed to start and stop.
             If not specified, self.prange or all timeslices are used.
         silent : bool
             Decides whether output is printed to the standard output.
@@ -641,6 +641,11 @@ class Corr:
                 fitrange = self.prange
             else:
                 fitrange = [0, self.T - 1]
+        else:
+            if not isinstance(fitrange, list):
+                raise Exception("fitrange has to be a list with two elements")
+            if len(fitrange) != 2:
+                raise Exception("fitrange has to have exactly two elements [fit_start, fit_stop]")
 
         xs = [x for x in range(fitrange[0], fitrange[1] + 1) if not self.content[x] is None]
         ys = [self.content[x][0] for x in range(fitrange[0], fitrange[1] + 1) if not self.content[x] is None]
diff --git a/tests/correlators_test.py b/tests/correlators_test.py
index 581705fd..9a2e7ea1 100644
--- a/tests/correlators_test.py
+++ b/tests/correlators_test.py
@@ -135,6 +135,11 @@ def test_fit_correlator():
     assert fit_res[0] == my_corr[0]
     assert fit_res[1] == my_corr[1] - my_corr[0]
 
+    with pytest.raises(Exception):
+        my_corr.fit(f, "from 0 to 3")
+    with pytest.raises(Exception):
+        my_corr.fit(f, [0, 2, 3])
+
 
 def test_plateau():
     my_corr = pe.correlators.Corr([pe.pseudo_Obs(1.01324, 0.05, 't'), pe.pseudo_Obs(1.042345, 0.008, 't')])