diff --git a/lib/isc/thread_p.h b/lib/isc/thread_p.h
index 0fd02a9684..b31e6c3038 100644
--- a/lib/isc/thread_p.h
+++ b/lib/isc/thread_p.h
@@ -17,6 +17,14 @@
 
 /*! \file */
 
+/*
+ * The current default stack sizes are as follows:
+ * - Linux glibc: 8MB
+ * - Linux musl: 128kB
+ * - FreeBSD: 2MB
+ * - OpenBSD: 512kB
+ * - NetBSD: 4MB
+ */
 #ifndef THREAD_MINSTACKSIZE
 #define THREAD_MINSTACKSIZE (1U * 1024 * 1024)
 #endif /* ifndef THREAD_MINSTACKSIZE */