diff --git a/pynestml/codegeneration/resources_nest/point_neuron/common/NeuronClass.jinja2 b/pynestml/codegeneration/resources_nest/point_neuron/common/NeuronClass.jinja2
index 9aee4c9cc..404e89d1e 100644
--- a/pynestml/codegeneration/resources_nest/point_neuron/common/NeuronClass.jinja2
+++ b/pynestml/codegeneration/resources_nest/point_neuron/common/NeuronClass.jinja2
@@ -1114,12 +1114,17 @@ void {{ neuronName }}::handle(nest::SpikeEvent &e)
   }
   else
   {
+    // Get the buffer index for inhibitory port
     nestml_buffer_idx = std::get<1>(rport_to_nestml_buffer_idx[e.get_rport()]);
-    if ( nestml_buffer_idx == {{ neuronName }}::PORT_NOT_AVAILABLE )
+    if ( nestml_buffer_idx != {{ neuronName }}::PORT_NOT_AVAILABLE )
     {
+      weight = -weight;
+    }
+    else
+    {
+      // spiking input port with negative weight, no change in the sign of weight
       nestml_buffer_idx = std::get<0>(rport_to_nestml_buffer_idx[e.get_rport()]);
     }
-    weight = -weight;
   }
 {%- endif %}
   B_.spike_inputs_[ nestml_buffer_idx - MIN_SPIKE_RECEPTOR ].add_value(
diff --git a/tests/nest_tests/input_ports_test.py b/tests/nest_tests/input_ports_test.py
index 0d26c79ad..888c78259 100644
--- a/tests/nest_tests/input_ports_test.py
+++ b/tests/nest_tests/input_ports_test.py
@@ -87,16 +87,16 @@ def test_input_ports(self):
         connections = nest.GetConnections(target=neuron)
 
         # corresponds to ``bar += NMDA_spikes + 2 * AMPA_spikes - 3 * GABA_spikes`` in the update block
-        assert events["bar"][-1] == len(spike_times[0]) * abs(connections.get("weight")[0]) \
+        assert events["bar"][-1] == len(spike_times[0]) * connections.get("weight")[0] \
                + 2 * len(spike_times[1]) * abs(connections.get("weight")[1]) \
                - 3 * len(spike_times[2]) * abs(connections.get("weight")[2])
 
         # corresponds to ``foo_spikes += foo[0] + 5.5 * foo[1]`` in the update block
-        assert events["foo_spikes"][-1] == len(spike_times[3]) * abs(connections.get("weight")[3]) \
+        assert events["foo_spikes"][-1] == len(spike_times[3]) * connections.get("weight")[3] \
                + 5.5 * len(spike_times[4]) * abs(connections.get("weight")[4])
 
         # corresponds to ``my_spikes_ip += my_spikes[0] + my_spikes[1] - my_spikes2[1]`` in the update block
-        assert events["my_spikes_ip"][-1] == len(spike_times[5]) * abs(connections.get("weight")[5]) \
+        assert events["my_spikes_ip"][-1] == len(spike_times[5]) * connections.get("weight")[5] \
                + len(spike_times[6]) * abs(connections.get("weight")[6]) \
                - len(spike_times[7]) * abs(connections.get("weight")[7])
 
diff --git a/tests/nest_tests/resources/iaf_psc_exp_multisynapse.nestml b/tests/nest_tests/resources/iaf_psc_exp_multisynapse.nestml
index 2c73778ba..e05b89249 100644
--- a/tests/nest_tests/resources/iaf_psc_exp_multisynapse.nestml
+++ b/tests/nest_tests/resources/iaf_psc_exp_multisynapse.nestml
@@ -21,7 +21,7 @@ model iaf_psc_exp_multisynapse_neuron:
         kernel I_kernel2 = (e / tau_syn2) * t * exp(-t / tau_syn2)
         kernel I_kernel3 = -exp(-t / tau_syn3)
 
-        recordable inline I_syn pA = (convolve(I_kernel1, spikes1) - convolve(I_kernel2, spikes2) + convolve(I_kernel3, spikes3)) * pA
+        recordable inline I_syn pA = (convolve(I_kernel1, spikes1) + convolve(I_kernel2, spikes2) + convolve(I_kernel3, spikes3)) * pA
 
         V_m' = -(V_m - E_L) / tau_m + (I_syn + I_e + I_stim) / C_m
 
diff --git a/tests/nest_tests/resources/iaf_psc_exp_multisynapse_vectors.nestml b/tests/nest_tests/resources/iaf_psc_exp_multisynapse_vectors.nestml
index 305fcf53e..6219c2681 100644
--- a/tests/nest_tests/resources/iaf_psc_exp_multisynapse_vectors.nestml
+++ b/tests/nest_tests/resources/iaf_psc_exp_multisynapse_vectors.nestml
@@ -21,7 +21,7 @@ model iaf_psc_exp_multisynapse_vectors_neuron:
         kernel I_kernel2 = exp(-1/tau_syn2*t)
         kernel I_kernel3 = -exp(-1/tau_syn3*t)
 
-        inline I_syn pA = (convolve(I_kernel1, spikes[0]) - convolve(I_kernel2, spikes[1]) + convolve(I_kernel3, spikes[2])) * pA
+        inline I_syn pA = (convolve(I_kernel1, spikes[0]) + convolve(I_kernel2, spikes[1]) + convolve(I_kernel3, spikes[2])) * pA
 
         V_m' = -(V_m - E_L) / tau_m + (I_syn + I_e + I_stim) / C_m
 
diff --git a/tests/nest_tests/test_multisynapse.py b/tests/nest_tests/test_multisynapse.py
index 60fc50abe..b9c47061a 100644
--- a/tests/nest_tests/test_multisynapse.py
+++ b/tests/nest_tests/test_multisynapse.py
@@ -69,7 +69,7 @@ def test_multisynapse(self):
         nest.Connect(sg, neuron, syn_spec={"receptor_type": receptor_types["SPIKES1"], "weight": 1000., "delay": 0.1})
 
         sg2 = nest.Create("spike_generator", params={"spike_times": [40., 60.]})
-        nest.Connect(sg2, neuron, syn_spec={"receptor_type": receptor_types["SPIKES2"], "weight": 1000., "delay": 0.1})
+        nest.Connect(sg2, neuron, syn_spec={"receptor_type": receptor_types["SPIKES2"], "weight": -1000., "delay": 0.1})
 
         sg3 = nest.Create("spike_generator", params={"spike_times": [30., 70.]})
         nest.Connect(sg3, neuron, syn_spec={"receptor_type": receptor_types["SPIKES3"], "weight": 500., "delay": 0.1})
@@ -150,7 +150,7 @@ def test_multisynapse_with_vector_input_ports(self):
         nest.Connect(sg, neuron, syn_spec={"receptor_type": receptor_types["SPIKES_0"], "weight": 1000., "delay": 0.1})
 
         sg2 = nest.Create("spike_generator", params={"spike_times": [40., 60.]})
-        nest.Connect(sg2, neuron, syn_spec={"receptor_type": receptor_types["SPIKES_1"], "weight": 1000., "delay": 0.1})
+        nest.Connect(sg2, neuron, syn_spec={"receptor_type": receptor_types["SPIKES_1"], "weight": -1000., "delay": 0.1})
 
         sg3 = nest.Create("spike_generator", params={"spike_times": [30., 70.]})
         nest.Connect(sg3, neuron, syn_spec={"receptor_type": receptor_types["SPIKES_2"], "weight": 500., "delay": 0.1})