diff --git a/ChangeLog b/ChangeLog
index db408c729e..4b8890eb74 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2016-03-20  Samuel Thibault  <samuel.thibault@ens-lyon.org>:
+
+	* sysdeps/mach/hurd/libc-lock.h (_IO_lock_inexpensive): Define to 1.
+
 2016-03-20  Samuel Thibault  <samuel.thibault@ens-lyon.org>:
 
 	* sysdeps/generic/dl-fcntl.h: New file, adds attribute_hidden to __open
diff --git a/sysdeps/mach/hurd/libc-lock.h b/sysdeps/mach/hurd/libc-lock.h
index f6cbe50fc2..dfcbee195c 100644
--- a/sysdeps/mach/hurd/libc-lock.h
+++ b/sysdeps/mach/hurd/libc-lock.h
@@ -23,6 +23,9 @@
 #include <cthreads.h>
 #include <hurd/threadvar.h>
 
+/* The locking here is very inexpensive, even for inlining.  */
+#define _IO_lock_inexpensive  1
+
 typedef struct mutex __libc_lock_t;
 typedef struct
 {