diff --git a/src/macros.rs b/src/macros.rs
index 0149b1fd1846..5c5b8c2deac7 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -402,6 +402,21 @@ macro_rules! offset_of {
     }};
 }
 
+/// Defines constants with an accompanying doc comment pointing out their
+/// instability, and links to the crate documentation for usage guidelines.
+macro_rules! ct {
+    ($($it:item)+) => {
+$(
+/// This constant, among others often used in C for the purposes of denoting the
+/// latest value or limit in a set of constants, is likely to change upstream.
+/// For correct usage, see the [crate-level documentation][docs].
+///
+/// [docs]: index.html#usage-recommendations
+$it
+)+
+    };
+}
+
 #[cfg(test)]
 mod tests {
     use core::any::TypeId;
diff --git a/src/unix/bsd/apple/mod.rs b/src/unix/bsd/apple/mod.rs
index f0bd543bf6df..51092ba30986 100644
--- a/src/unix/bsd/apple/mod.rs
+++ b/src/unix/bsd/apple/mod.rs
@@ -3733,7 +3733,11 @@ pub const MNT_NOWAIT: c_int = 2;
 
 // <mach/thread_policy.h>
 pub const THREAD_STANDARD_POLICY: c_int = 1;
-pub const THREAD_STANDARD_POLICY_COUNT: c_int = 0;
+
+ct! {
+    pub const THREAD_STANDARD_POLICY_COUNT: c_int = 0;
+}
+
 pub const THREAD_EXTENDED_POLICY: c_int = 1;
 pub const THREAD_TIME_CONSTRAINT_POLICY: c_int = 2;
 pub const THREAD_PRECEDENCE_POLICY: c_int = 3;
@@ -3795,7 +3799,11 @@ pub const VM_PAGE_QUERY_PAGE_CS_NX: i32 = 0x400;
 
 // mach/task_info.h
 pub const TASK_THREAD_TIMES_INFO: u32 = 3;
-pub const HOST_CPU_LOAD_INFO_COUNT: u32 = 4;
+
+ct! {
+    pub const HOST_CPU_LOAD_INFO_COUNT: u32 = 4;
+}
+
 pub const MACH_TASK_BASIC_INFO: u32 = 20;
 
 pub const MACH_PORT_NULL: i32 = 0;
@@ -3858,7 +3866,10 @@ pub const COPYFILE_STATE_DST_BSIZE: c_int = 12;
 pub const COPYFILE_STATE_BSIZE: c_int = 13;
 
 // <sys/attr.h>
-pub const ATTR_BIT_MAP_COUNT: c_ushort = 5;
+ct! {
+    pub const ATTR_BIT_MAP_COUNT: c_ushort = 5;
+}
+
 pub const FSOPT_NOFOLLOW: u32 = 0x1;
 pub const FSOPT_NOFOLLOW_ANY: u32 = 0x800;
 pub const FSOPT_REPORT_FULLSIZE: u32 = 0x4;
@@ -4029,38 +4040,40 @@ const fn __DARWIN_ALIGN32(p: usize) -> usize {
     (p + __DARWIN_ALIGNBYTES32) & !__DARWIN_ALIGNBYTES32
 }
 
-pub const THREAD_EXTENDED_POLICY_COUNT: mach_msg_type_number_t =
-    (size_of::<thread_extended_policy_data_t>() / size_of::<integer_t>()) as mach_msg_type_number_t;
-pub const THREAD_TIME_CONSTRAINT_POLICY_COUNT: mach_msg_type_number_t =
-    (size_of::<thread_time_constraint_policy_data_t>() / size_of::<integer_t>())
-        as mach_msg_type_number_t;
-pub const THREAD_PRECEDENCE_POLICY_COUNT: mach_msg_type_number_t =
-    (size_of::<thread_precedence_policy_data_t>() / size_of::<integer_t>())
-        as mach_msg_type_number_t;
-pub const THREAD_AFFINITY_POLICY_COUNT: mach_msg_type_number_t =
-    (size_of::<thread_affinity_policy_data_t>() / size_of::<integer_t>()) as mach_msg_type_number_t;
-pub const THREAD_BACKGROUND_POLICY_COUNT: mach_msg_type_number_t =
-    (size_of::<thread_background_policy_data_t>() / size_of::<integer_t>())
-        as mach_msg_type_number_t;
-pub const THREAD_LATENCY_QOS_POLICY_COUNT: mach_msg_type_number_t =
-    (size_of::<thread_latency_qos_policy_data_t>() / size_of::<integer_t>())
-        as mach_msg_type_number_t;
-pub const THREAD_THROUGHPUT_QOS_POLICY_COUNT: mach_msg_type_number_t =
-    (size_of::<thread_throughput_qos_policy_data_t>() / size_of::<integer_t>())
-        as mach_msg_type_number_t;
-pub const THREAD_BASIC_INFO_COUNT: mach_msg_type_number_t =
-    (size_of::<thread_basic_info_data_t>() / size_of::<integer_t>()) as mach_msg_type_number_t;
-pub const THREAD_IDENTIFIER_INFO_COUNT: mach_msg_type_number_t =
-    (size_of::<thread_identifier_info_data_t>() / size_of::<integer_t>()) as mach_msg_type_number_t;
-pub const THREAD_EXTENDED_INFO_COUNT: mach_msg_type_number_t =
-    (size_of::<thread_extended_info_data_t>() / size_of::<integer_t>()) as mach_msg_type_number_t;
-
-pub const TASK_THREAD_TIMES_INFO_COUNT: u32 =
-    (size_of::<task_thread_times_info_data_t>() / size_of::<natural_t>()) as u32;
-pub const MACH_TASK_BASIC_INFO_COUNT: u32 =
-    (size_of::<mach_task_basic_info_data_t>() / size_of::<natural_t>()) as u32;
-pub const HOST_VM_INFO64_COUNT: mach_msg_type_number_t =
-    (size_of::<vm_statistics64_data_t>() / size_of::<integer_t>()) as mach_msg_type_number_t;
+ct! {
+    pub const THREAD_EXTENDED_POLICY_COUNT: mach_msg_type_number_t =
+        (size_of::<thread_extended_policy_data_t>() / size_of::<integer_t>()) as mach_msg_type_number_t;
+    pub const THREAD_TIME_CONSTRAINT_POLICY_COUNT: mach_msg_type_number_t =
+        (size_of::<thread_time_constraint_policy_data_t>() / size_of::<integer_t>())
+            as mach_msg_type_number_t;
+    pub const THREAD_PRECEDENCE_POLICY_COUNT: mach_msg_type_number_t =
+        (size_of::<thread_precedence_policy_data_t>() / size_of::<integer_t>())
+            as mach_msg_type_number_t;
+    pub const THREAD_AFFINITY_POLICY_COUNT: mach_msg_type_number_t =
+        (size_of::<thread_affinity_policy_data_t>() / size_of::<integer_t>()) as mach_msg_type_number_t;
+    pub const THREAD_BACKGROUND_POLICY_COUNT: mach_msg_type_number_t =
+        (size_of::<thread_background_policy_data_t>() / size_of::<integer_t>())
+            as mach_msg_type_number_t;
+    pub const THREAD_LATENCY_QOS_POLICY_COUNT: mach_msg_type_number_t =
+        (size_of::<thread_latency_qos_policy_data_t>() / size_of::<integer_t>())
+            as mach_msg_type_number_t;
+    pub const THREAD_THROUGHPUT_QOS_POLICY_COUNT: mach_msg_type_number_t =
+        (size_of::<thread_throughput_qos_policy_data_t>() / size_of::<integer_t>())
+            as mach_msg_type_number_t;
+    pub const THREAD_BASIC_INFO_COUNT: mach_msg_type_number_t =
+        (size_of::<thread_basic_info_data_t>() / size_of::<integer_t>()) as mach_msg_type_number_t;
+    pub const THREAD_IDENTIFIER_INFO_COUNT: mach_msg_type_number_t =
+        (size_of::<thread_identifier_info_data_t>() / size_of::<integer_t>()) as mach_msg_type_number_t;
+    pub const THREAD_EXTENDED_INFO_COUNT: mach_msg_type_number_t =
+        (size_of::<thread_extended_info_data_t>() / size_of::<integer_t>()) as mach_msg_type_number_t;
+
+    pub const TASK_THREAD_TIMES_INFO_COUNT: u32 =
+        (size_of::<task_thread_times_info_data_t>() / size_of::<natural_t>()) as u32;
+    pub const MACH_TASK_BASIC_INFO_COUNT: u32 =
+        (size_of::<mach_task_basic_info_data_t>() / size_of::<natural_t>()) as u32;
+    pub const HOST_VM_INFO64_COUNT: mach_msg_type_number_t =
+        (size_of::<vm_statistics64_data_t>() / size_of::<integer_t>()) as mach_msg_type_number_t;
+}
 
 // bsd/net/if_mib.h
 /// Non-interface-specific
diff --git a/src/unix/linux_like/android/mod.rs b/src/unix/linux_like/android/mod.rs
index b262ff8a142c..0978c7fe6f15 100644
--- a/src/unix/linux_like/android/mod.rs
+++ b/src/unix/linux_like/android/mod.rs
@@ -1569,7 +1569,10 @@ pub const NFNL_SUBSYS_CTNETLINK_TIMEOUT: c_int = 8;
 pub const NFNL_SUBSYS_CTHELPER: c_int = 9;
 pub const NFNL_SUBSYS_NFTABLES: c_int = 10;
 pub const NFNL_SUBSYS_NFT_COMPAT: c_int = 11;
-pub const NFNL_SUBSYS_COUNT: c_int = 12;
+
+ct! {
+    pub const NFNL_SUBSYS_COUNT: c_int = 12;
+}
 
 pub const NFNL_MSG_BATCH_BEGIN: c_int = NLMSG_MIN_TYPE;
 pub const NFNL_MSG_BATCH_END: c_int = NLMSG_MIN_TYPE + 1;
diff --git a/src/unix/linux_like/linux/mod.rs b/src/unix/linux_like/linux/mod.rs
index 081b16d78ce3..a448ee896826 100644
--- a/src/unix/linux_like/linux/mod.rs
+++ b/src/unix/linux_like/linux/mod.rs
@@ -1899,7 +1899,10 @@ pub const NFNL_SUBSYS_CTHELPER: c_int = 9;
 pub const NFNL_SUBSYS_NFTABLES: c_int = 10;
 pub const NFNL_SUBSYS_NFT_COMPAT: c_int = 11;
 pub const NFNL_SUBSYS_HOOK: c_int = 12;
-pub const NFNL_SUBSYS_COUNT: c_int = 13;
+
+ct! {
+    pub const NFNL_SUBSYS_COUNT: c_int = 13;
+}
 
 pub const NFNL_MSG_BATCH_BEGIN: c_int = crate::NLMSG_MIN_TYPE;
 pub const NFNL_MSG_BATCH_END: c_int = crate::NLMSG_MIN_TYPE + 1;
diff --git a/src/unix/solarish/illumos.rs b/src/unix/solarish/illumos.rs
index b31c31bd1f6c..54826eb94934 100644
--- a/src/unix/solarish/illumos.rs
+++ b/src/unix/solarish/illumos.rs
@@ -186,7 +186,10 @@ pub const PRIV_USER: c_uint = PRIV_DEBUG
     | PRIV_AWARE_RESET
     | PRIV_PFEXEC;
 
-pub const LGRP_RSRC_COUNT: crate::lgrp_rsrc_t = 2;
+ct! {
+    pub const LGRP_RSRC_COUNT: crate::lgrp_rsrc_t = 2;
+}
+
 pub const LGRP_RSRC_CPU: crate::lgrp_rsrc_t = 0;
 pub const LGRP_RSRC_MEM: crate::lgrp_rsrc_t = 1;