diff --git a/pvactools/tools/pvacvector/run.py b/pvactools/tools/pvacvector/run.py
index 1b5ea2a40..ebf52c9e7 100644
--- a/pvactools/tools/pvacvector/run.py
+++ b/pvactools/tools/pvacvector/run.py
@@ -257,6 +257,10 @@ def create_distance_matrix(Paths):
     return distance_matrix
 
 def find_optimal_path(graph, distance_matrix, seq_dict, base_output_dir, junctions_file, args):
+    (valid, error) = check_graph_valid(graph, seq_dict)
+    if not valid:
+        raise Exception("Invalid graph passed to find_optimal_path: {}".format(error))
+
     init_state = sorted(graph.nodes())
     if not os.environ.get('TEST_FLAG') or os.environ.get('TEST_FLAG') == '0':
         random.shuffle(init_state)
diff --git a/tests/test_pvacvector.py b/tests/test_pvacvector.py
index 62b2a50d0..be239d551 100644
--- a/tests/test_pvacvector.py
+++ b/tests/test_pvacvector.py
@@ -464,6 +464,29 @@ def test_pvacvector_remove_peptides(self):
 
         output_dir.cleanup()
 
+    def test_find_optimal_path_raises_on_invalid_graph(self):
+        with tempfile.TemporaryDirectory() as output_dir:
+            seq_dict = {"MT.TEST.1": "SYFPEITHI"}
+            graph = run.initialize_graph(seq_dict.keys())
+            distance_matrix = run.create_distance_matrix(graph)
+            junctions_file = run.write_junctions_file(graph, output_dir)
+            args = argparse.Namespace(
+                spacers=["None"],
+                sample_name="single_peptide_no_edges",
+            )
+
+            with self.assertRaises(Exception) as context:
+                run.find_optimal_path(
+                    graph,
+                    distance_matrix,
+                    seq_dict,
+                    output_dir,
+                    junctions_file,
+                    args,
+                )
+
+            self.assertIn("Invalid graph passed to find_optimal_path", str(context.exception))
+
     def test_prevent_clipping_best_peptide(self):
         output_dir = tempfile.TemporaryDirectory()
         input_file = os.path.join(self.test_data_dir, 'Test.vector.prevent_clipping_best_peptide.input.fa')