diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index 9871b9698..3b0e11187 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,8 @@
+2015-04-02  Jon TURNEY  <jon.turney@dronecode.org.uk>
+
+	* include/cygwin/signal.h (struct __mcontext): 16-byte align.
+	* include/sys/ucontext.h (ucontext_t): Ditto.
+
 2015-04-02  Corinna Vinschen  <corinna@vinschen.de>
 
 	* sec_acl.cc (CYG_ACE_ISBITS_TO_WIN): Fix typo.
diff --git a/winsup/cygwin/include/cygwin/signal.h b/winsup/cygwin/include/cygwin/signal.h
index 04e65aa34..ef29baf7b 100644
--- a/winsup/cygwin/include/cygwin/signal.h
+++ b/winsup/cygwin/include/cygwin/signal.h
@@ -49,7 +49,7 @@ struct _fpstate
   __uint32_t padding[24];
 };
 
-struct __mcontext
+struct __attribute__ ((aligned (16))) __mcontext
 {
   __uint64_t p1home;
   __uint64_t p2home;
diff --git a/winsup/cygwin/include/sys/ucontext.h b/winsup/cygwin/include/sys/ucontext.h
index 9362d90cd..65485fbad 100644
--- a/winsup/cygwin/include/sys/ucontext.h
+++ b/winsup/cygwin/include/sys/ucontext.h
@@ -15,11 +15,11 @@ details. */
 
 typedef struct __mcontext mcontext_t;
 
-typedef struct __ucontext {
+typedef __attribute__ ((aligned (16))) struct __ucontext {
+	mcontext_t	uc_mcontext;
 	struct __ucontext *uc_link;
 	sigset_t	uc_sigmask;
 	stack_t	uc_stack;
-	mcontext_t	uc_mcontext;
 	unsigned long int	uc_flags;
 } ucontext_t;