diff --git a/pysyncon/dataprep.py b/pysyncon/dataprep.py
index b78a566..f35f431 100644
--- a/pysyncon/dataprep.py
+++ b/pysyncon/dataprep.py
@@ -131,6 +131,11 @@ def __init__(
             raise ValueError(f"time_variable {time_variable} not in foo columns.")
         self.time_variable = time_variable
 
+        if foo[[unit_variable, time_variable]].duplicated().any():
+            raise ValueError(
+                "Multiple rows found in `foo` for same [unit, time] pairs."
+            )
+
         if isinstance(treatment_identifier, (list, tuple)):
             for treated in treatment_identifier:
                 # This throws FutureWarning (see https://stackoverflow.com/a/46721064/11594901)
@@ -169,7 +174,14 @@ def __init__(
                 )
         self.controls_identifier = controls_identifier
 
+        if self.foo[self.foo[self.time_variable].isin(time_predictors_prior)].empty:
+            raise ValueError(
+                f"foo has no rows in the time range `time_predictors_prior`."
+            )
         self.time_predictors_prior = time_predictors_prior
+
+        if self.foo[self.foo[self.time_variable].isin(time_optimize_ssr)].empty:
+            raise ValueError(f"foo has no rows in the time range `time_optimize_ssr`.")
         self.time_optimize_ssr = time_optimize_ssr
 
         if special_predictors:
@@ -178,11 +190,15 @@ def __init__(
                     raise ValueError(
                         "Elements of special_predictors should be tuples of length 3."
                     )
-                predictor, _, op = el
+                predictor, time_range, op = el
                 if predictor not in foo.columns:
                     raise ValueError(
                         f"{predictor} in special_predictors not in foo columns."
                     )
+                if self.foo[self.foo[self.time_variable].isin(time_range)].empty:
+                    raise ValueError(
+                        f"foo has no rows in the time range {time_range} for `special_predictor` {el}."
+                    )
                 if op not in AGG_OP:
                     agg_op_str = ", ".join([f'"{o}"' for o in AGG_OP])
                     raise ValueError(
diff --git a/tests/test_dataprep.py b/tests/test_dataprep.py
index 5acc377..f31f46f 100644
--- a/tests/test_dataprep.py
+++ b/tests/test_dataprep.py
@@ -157,6 +157,27 @@ def test_init_arg_time_variable(self):
 
         self.assertRaises(ValueError, Dataprep, time_variable="badval", **kwargs)
 
+    def test_init_multiple_rows(self):
+        kwargs = {
+            "predictors": self.predictors,
+            "predictors_op": self.predictors_op,
+            "dependent": self.dependent,
+            "unit_variable": self.unit_variable,
+            "time_variable": self.time_variable,
+            "treatment_identifier": self.treatment_identifier,
+            "controls_identifier": self.controls_identifier,
+            "time_predictors_prior": self.time_predictors_prior,
+            "time_optimize_ssr": self.time_optimize_ssr,
+            "special_predictors": self.special_predictors,
+        }
+
+        self.assertRaises(
+            ValueError,
+            Dataprep,
+            foo=pd.concat([self.foo, self.foo.iloc[0:1]], axis=0),
+            **kwargs,
+        )
+
     def test_init_arg_treatment_identifier(self):
         kwargs = {
             "foo": self.foo,
@@ -176,6 +197,61 @@ def test_init_arg_treatment_identifier(self):
             ValueError, Dataprep, treatment_identifier=["badval"], **kwargs
         )
 
+    def test_bad_time_periods_time_predictors_prior(self):
+        kwargs = {
+            "foo": self.foo,
+            "predictors": self.predictors,
+            "predictors_op": self.predictors_op,
+            "dependent": self.dependent,
+            "unit_variable": self.unit_variable,
+            "time_variable": self.time_variable,
+            "controls_identifier": self.controls_identifier,
+            "time_optimize_ssr": self.time_optimize_ssr,
+            "treatment_identifier": self.treatment_identifier,
+            "special_predictors": self.special_predictors,
+        }
+
+        self.assertRaises(
+            ValueError, Dataprep, time_predictors_prior=["2", "3"], **kwargs
+        )
+
+    def test_bad_time_periods_time_optimize_ssr(self):
+        kwargs = {
+            "foo": self.foo,
+            "predictors": self.predictors,
+            "predictors_op": self.predictors_op,
+            "dependent": self.dependent,
+            "unit_variable": self.unit_variable,
+            "time_variable": self.time_variable,
+            "controls_identifier": self.controls_identifier,
+            "time_predictors_prior": self.time_predictors_prior,
+            "treatment_identifier": self.treatment_identifier,
+            "special_predictors": self.special_predictors,
+        }
+
+        self.assertRaises(ValueError, Dataprep, time_optimize_ssr=["2", "3"], **kwargs)
+
+    def test_bad_time_periods_special_predictors(self):
+        kwargs = {
+            "foo": self.foo,
+            "predictors": self.predictors,
+            "predictors_op": self.predictors_op,
+            "dependent": self.dependent,
+            "unit_variable": self.unit_variable,
+            "time_variable": self.time_variable,
+            "controls_identifier": self.controls_identifier,
+            "time_optimize_ssr": self.time_optimize_ssr,
+            "time_predictors_prior": self.time_predictors_prior,
+            "treatment_identifier": self.treatment_identifier,
+        }
+
+        self.assertRaises(
+            ValueError,
+            Dataprep,
+            special_predictors=[("predictor1", ["2"], "mean")],
+            **kwargs,
+        )
+
     def test_init_arg_controls_identifier(self):
         kwargs = {
             "foo": self.foo,