diff --git a/man2/seccomp.2 b/man2/seccomp.2
index febbd8043..ce9b6367c 100644
--- a/man2/seccomp.2
+++ b/man2/seccomp.2
@@ -983,7 +983,9 @@ install_filter(int syscall_nr, int t_arch, int f_errno)
 {
     unsigned int upper_nr_limit = 0xffffffff;
 
-    /* Assume that AUDIT_ARCH_X86_64 means the normal x86-64 ABI */
+    /* Assume that AUDIT_ARCH_X86_64 means the normal x86-64 ABI
+       (in the x32 ABI, all system calls have bit 30 set in the
+       'nr' field, meaning the numbers are >= X32_SYSCALL_BIT) */
     if (t_arch == AUDIT_ARCH_X86_64)
         upper_nr_limit = X32_SYSCALL_BIT - 1;