diff --git a/src/inifix/_cli.py b/src/inifix/_cli.py
index 589b467..7fd7773 100644
--- a/src/inifix/_cli.py
+++ b/src/inifix/_cli.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import os
+import sys
 from typing import Literal, NamedTuple, TextIO
 
 
@@ -17,4 +18,14 @@ class TaskResults(NamedTuple):
 def get_cpu_count() -> int:
     # this function exists primarily to be mocked
     # instead of something we don't own
-    return os.cpu_count() or 1
+    base_cpu_count: int | None
+    if sys.version_info >= (3, 13):
+        base_cpu_count = os.process_cpu_count()
+    else:
+        if hasattr(os, "sched_getaffinity"):
+            # this function isn't available on all platforms
+            base_cpu_count = len(os.sched_getaffinity(0))
+        else:
+            # this proxy is good enough in most situations
+            base_cpu_count = os.cpu_count()
+    return base_cpu_count or 1