diff --git a/libc/include/limits.h b/libc/include/limits.h
index 69df082..6ae629b 100644
--- a/libc/include/limits.h
+++ b/libc/include/limits.h
@@ -97,4 +97,5 @@
 /* POSIX says these belong in <unistd.h> but BSD has some in <limits.h>. */
 #include <machine/posix_limits.h>
 
+#define HOST_NAME_MAX _POSIX_HOST_NAME_MAX
 #endif /* !_LIMITS_H_ */
diff --git a/libc/include/machine/posix_limits.h b/libc/include/machine/posix_limits.h
index f906e3b..f092731 100644
--- a/libc/include/machine/posix_limits.h
+++ b/libc/include/machine/posix_limits.h
@@ -37,6 +37,7 @@
 #define _POSIX_CHOWN_RESTRICTED     1  /* yes, chown requires appropriate privileges */
 #define _POSIX_FSYNC                1  /* fdatasync() supported */
 #define _POSIX_JOB_CONTROL          1  /* job control is a Linux feature */
+#define _POSIX_HOST_NAME_MAX        255
 #define _POSIX_LINK_MAX             8
 #define _POSIX_LOGIN_NAME_MAX       9  /* includes trailing NUL */
 #define _POSIX_MAPPED_FILES         1  /* mmap-ed files supported */