diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index 494991140..bf78e2a98 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,7 @@
+2015-02-23  Corinna Vinschen  <corinna@vinschen.de>
+
+	* winsup.h (SIGTOMASK): Add cast to sigset_t to avoid int overflow.
+
 2015-02-20  Corinna Vinschen  <corinna@vinschen.de>
 
 	* grp.cc (internal_getgroups): Take additional timeout_ns parameter.
diff --git a/winsup/cygwin/release/1.7.35 b/winsup/cygwin/release/1.7.35
index 8c8c9962d..564698907 100644
--- a/winsup/cygwin/release/1.7.35
+++ b/winsup/cygwin/release/1.7.35
@@ -35,3 +35,6 @@ Bug Fixes
 
 - 64 bit: Export forgotten symbol __mempcpy.
   Addresses: https://cygwin.com/ml/cygwin/2015-02/msg00394.html
+
+- 64 bit: Avoid misbehaviour in signal mask computation.
+  Addresses: https://cygwin.com/ml/cygwin/2015-02/msg00665.html
diff --git a/winsup/cygwin/winsup.h b/winsup/cygwin/winsup.h
index d61f6950f..4b549dde9 100644
--- a/winsup/cygwin/winsup.h
+++ b/winsup/cygwin/winsup.h
@@ -131,7 +131,7 @@ extern int cygserver_running;
     })
 
 /* Convert a signal to a signal mask */
-#define SIGTOMASK(sig)	(1 << ((sig) - 1))
+#define SIGTOMASK(sig)	((sigset_t) 1 << ((sig) - 1))
 
 #define set_api_fatal_return(n) do {extern int __api_fatal_exit_val; __api_fatal_exit_val = (n);} while (0)