diff --git a/python/cirron/cirron.py b/python/cirron/cirron.py
index 86f9242..56efd5b 100644
--- a/python/cirron/cirron.py
+++ b/python/cirron/cirron.py
@@ -44,6 +44,9 @@ def __repr__(self):
         )
 
 
+overhead = {}
+
+
 class Collector:
     cirron_lib = CDLL(lib_path)
     cirron_lib.start.argtypes = None
@@ -55,6 +58,23 @@ def __init__(self):
         self._fd = None
         self.counters = Counter()
 
+        # We try to estimate what the overhead of the collector is, taking the minimum
+        # of 10 runs.
+        global overhead
+        if not overhead:
+            collector = Collector()
+            for _ in range(10):
+                with Collector() as collector:
+                    pass
+
+                for field, _ in Counter._fields_:
+                    if field not in overhead:
+                        overhead[field] = getattr(collector.counters, field)
+                    else:
+                        overhead[field] = min(
+                            overhead[field], getattr(collector.counters, field)
+                        )
+
     def __enter__(self):
         ret_val = Collector.cirron_lib.start()
         if ret_val == -1:
@@ -80,21 +100,3 @@ def __exit__(self, exc_type, exc_value, traceback):
                     )
                 else:
                     setattr(self.counters, field, 0)
-
-
-# We try to estimate what the overhead of the collector is, taking the minimum
-# of 10 runs.
-overhead = {}
-collector = Collector()
-o = {}
-for _ in range(10):
-    with Collector() as collector:
-        pass
-
-    for field, _ in Counter._fields_:
-        if field not in overhead:
-            o[field] = getattr(collector.counters, field)
-        else:
-            o[field] = min(overhead[field], getattr(collector.counters, field))
-overhead = o
-del collector
diff --git a/python/tests/tests.py b/python/tests/tests.py
index 8445e12..da24896 100644
--- a/python/tests/tests.py
+++ b/python/tests/tests.py
@@ -1,7 +1,9 @@
 import unittest
 import os
+
 from cirron import Tracer, Collector
 
+
 class Test(unittest.TestCase):
     def test_tracer(self):
         with Tracer() as t:
@@ -9,7 +11,10 @@ def test_tracer(self):
 
         self.assertEqual(len(t.trace), 3)
 
-    @unittest.skipIf("GITHUB_ACTIONS" in os.environ, "As of 02/07/2024, GitHub Actions does not support perf_event_open.")
+    @unittest.skipIf(
+        "GITHUB_ACTIONS" in os.environ,
+        "As of 02/07/2024, GitHub Actions does not support perf_event_open.",
+    )
     def test_collector(self):
         with Collector() as c:
             print(0)