diff --git a/tools/fuzz_test/graph.py b/tools/fuzz_test/graph.py
index 099859b..d7fbda0 100644
--- a/tools/fuzz_test/graph.py
+++ b/tools/fuzz_test/graph.py
@@ -82,15 +82,14 @@ def parse_graph(path):
     outputs = set()
     built_by = {}
     with open(path, 'r') as f:
-        data = json.loads(f.read())
+        data = json.load(f)
         for file in data["files"]:
             files[file['id']] = file
         for proc in data["procs"]:
-            proc_in = set(proc.get('input', []))
             proc_out = set(proc.get('output', []))
             
-            inputs = inputs | proc_in
-            outputs = outputs | proc_out
+            inputs.update(proc.get("input", []))
+            outputs.update(proc_out)
             image = os.path.basename(files[proc['image']]['name'])
             for output in proc_out:
                 built_by[files[output]['name']] = image