diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -4838,6 +4838,10 @@
     Py_RETURN_NONE;
 }
 
+#ifdef __arm__ /* Issue #12936 */
+    #undef HAVE_SCHED_SETAFFINITY
+#endif
+
 #ifdef HAVE_SCHED_SETAFFINITY
 
 typedef struct {