diff --git a/src/oemof/solph/components/_generic_storage.py b/src/oemof/solph/components/_generic_storage.py
index 1c34269ad..05a492216 100644
--- a/src/oemof/solph/components/_generic_storage.py
+++ b/src/oemof/solph/components/_generic_storage.py
@@ -1032,21 +1032,20 @@ def _create(self, group=None):
         # ########################## CHECKS ###################################
         if m.es.periods is not None:
             for n in group:
-                error = (
+                error_fixed_absolute_losses = (
                     "For a multi-period investment model, fixed absolute"
                     " losses are not supported. Please remove parameter."
                 )
                 if n.fixed_losses_absolute.default != 0:
-                    raise ValueError(error)
-                warning = (
+                    raise ValueError(error_fixed_absolute_losses)
+                error_initial_storage_level = (
                     "For a multi-period model, initial_storage_level is"
-                    " not supported.\nIt is suggested to remove that"
-                    " parameter since it has no effect.\nstorage_content"
-                    " will be zero, until there is some usable storage "
-                    " capacity installed."
+                    " not supported.\nIt needs to be removed since it"
+                    " has no effect.\nstorage_content will be zero,"
+                    " until there is some usable storage capacity installed."
                 )
                 if n.initial_storage_level is not None:
-                    warn(warning, debugging.SuspiciousUsageWarning)
+                    raise ValueError(error_initial_storage_level)
 
         # ########################## SETS #####################################
 
@@ -1315,10 +1314,8 @@ def _old_storage_capacity_rule(block):
             def _initially_empty_rule(block):
                 """Ensure storage to be empty initially"""
                 for n in self.INVESTSTORAGES:
-                    for t in m.TIMESTEPS:
-                        if t == 0:
-                            expr = self.storage_content[n, 0] == 0
-                            self.initially_empty.add((n, t), expr)
+                    expr = self.storage_content[n, 0] == 0
+                    self.initially_empty.add((n, 0), expr)
 
             self.initially_empty = Constraint(
                 self.INVESTSTORAGES, m.TIMESTEPS, noruleinit=True
diff --git a/tests/multi_period_constraint_tests.py b/tests/multi_period_constraint_tests.py
index ac776fc93..974e65e10 100644
--- a/tests/multi_period_constraint_tests.py
+++ b/tests/multi_period_constraint_tests.py
@@ -385,7 +385,6 @@ def test_storage_invest_2(self):
             investment=solph.Investment(
                 ep_costs=145, lifetime=20, existing=20, age=19
             ),
-            initial_storage_level=0.5,
         )
         self.energysystem.add(bel, storage)
         self.compare_lp_files("storage_invest_2_multi_period.lp")
@@ -612,7 +611,7 @@ def test_storage_invest_1_fixed_losses(self):
             self.get_om()
 
     def test_storage_invest_1_initial_storage_level(self):
-        """Test warning for initial storage level
+        """Test error for initial storage level
         with multi-period investments"""
         bel = solph.buses.Bus(label="electricityBus")
         storage = solph.components.GenericStorage(
@@ -642,14 +641,12 @@ def test_storage_invest_1_initial_storage_level(self):
         self.energysystem.add(bel, storage)
         msg = (
             "For a multi-period model, initial_storage_level is"
-            " not supported.\nIt is suggested to remove that"
-            " parameter since it has no effect.\nstorage_content"
-            " will be zero, until there is some usable storage "
-            " capacity installed."
+            " not supported.\nIt needs to be removed since it"
+            " has no effect.\nstorage_content will be zero,"
+            " until there is some usable storage capacity installed."
         )
-        with warnings.catch_warnings(record=True) as w:
+        with pytest.raises(ValueError, match=msg):
             self.get_om()
-            assert msg in str(w[1].message)
 
     def test_storage_invest_1_missing_lifetime(self):
         """Test error thrown if storage misses necessary lifetime"""