diff --git a/ChangeLog b/ChangeLog
index bb61911610..1d0d2fb221 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2017-06-09  Joseph Myers  <joseph@codesourcery.com>
+
+	[BZ #21560]
+	* posix/sys/wait.h: Condition include of <signal.h> on
+	[__USE_XOPEN_EXTENDED || __USE_XOPEN2K8].  Include <bits/types.h>
+	unconditionally.
+	[!__pid_t_defined] (pid_t): Define typedef.
+
 2017-06-09  Zack Weinberg  <zackw@panix.com>
 
 	* include/errno.h (__errno_location): Use __attribute_const__
diff --git a/posix/sys/wait.h b/posix/sys/wait.h
index d5b7e4d8d4..909979bc9d 100644
--- a/posix/sys/wait.h
+++ b/posix/sys/wait.h
@@ -26,7 +26,15 @@
 
 __BEGIN_DECLS
 
-#include <signal.h>
+#include <bits/types.h>
+#ifndef __pid_t_defined
+typedef __pid_t pid_t;
+# define __pid_t_defined
+#endif
+
+#if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K8
+# include <signal.h>
+#endif
 
 /* These macros could also be defined in <stdlib.h>.  */
 #if !defined _STDLIB_H || (!defined __USE_XOPEN && !defined __USE_XOPEN2K8)
@@ -98,7 +106,6 @@ extern __pid_t waitpid (__pid_t __pid, int *__stat_loc, int __options);
 
 #if defined __USE_XOPEN || defined __USE_XOPEN2K8
 # ifndef __id_t_defined
-#  include <bits/types.h>
 typedef __id_t id_t;
 #  define __id_t_defined
 # endif