diff --git a/include/uapi/linux/shm.h b/include/uapi/linux/shm.h
index 74e786de6f4e..1fbf24ea37fd 100644
--- a/include/uapi/linux/shm.h
+++ b/include/uapi/linux/shm.h
@@ -8,17 +8,20 @@
 #endif
 
 /*
- * SHMMAX, SHMMNI and SHMALL are upper limits are defaults which can
- * be modified by sysctl.
+ * SHMMNI, SHMMAX and SHMALL are default upper limits which can be
+ * modified by sysctl. The SHMMAX and SHMALL values have been chosen to
+ * be as large possible without facilitating scenarios where userspace
+ * causes overflows when adjusting the limits via operations of the form
+ * "retrieve current limit; add X; update limit". It is therefore not
+ * advised to make SHMMAX and SHMALL any larger. These limits are
+ * suitable for both 32 and 64-bit systems.
  */
-
 #define SHMMIN 1			 /* min shared seg size (bytes) */
 #define SHMMNI 4096			 /* max num of segs system wide */
-#define SHMMAX (ULONG_MAX - (1L<<24))	 /* max shared seg size (bytes) */
-#define SHMALL (ULONG_MAX - (1L<<24))	 /* max shm system wide (pages) */
+#define SHMMAX (ULONG_MAX - (1UL << 24)) /* max shared seg size (bytes) */
+#define SHMALL (ULONG_MAX - (1UL << 24)) /* max shm system wide (pages) */
 #define SHMSEG SHMMNI			 /* max shared segs per process */
 
-
 /* Obsolete, used only for backwards compatibility and libc5 compiles */
 struct shmid_ds {
 	struct ipc_perm		shm_perm;	/* operation perms */