diff --git a/ChangeLog b/ChangeLog
index 7e30bf4dca..a3543f8a31 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2020-05-28  Bruno Haible  <bruno@clisp.org>
+
+	pagealign_alloc: Make more robust in multithreaded applications.
+	* lib/pagealign_alloc.c (pagealign_alloc): Pass an O_CLOEXEC flag to
+	open().
+	* modules/pagealign_alloc (Depends-on): Add 'open'.
+
 2020-05-28  Bruno Haible  <bruno@clisp.org>
 
 	openat: Make more robust in multithreaded applications.
diff --git a/lib/pagealign_alloc.c b/lib/pagealign_alloc.c
index 1995e9c57e..3bd803e4a8 100644
--- a/lib/pagealign_alloc.c
+++ b/lib/pagealign_alloc.c
@@ -132,7 +132,7 @@ pagealign_alloc (size_t size)
   const int flags = MAP_FILE | MAP_PRIVATE;
   if (fd == -1)
     {
-      fd = open ("/dev/zero", O_RDONLY, 0666);
+      fd = open ("/dev/zero", O_RDONLY | O_CLOEXEC, 0666);
       if (fd < 0)
         error (EXIT_FAILURE, errno, _("Failed to open /dev/zero for read"));
     }
diff --git a/modules/pagealign_alloc b/modules/pagealign_alloc
index 5209b645f5..b97f9bb2fd 100644
--- a/modules/pagealign_alloc
+++ b/modules/pagealign_alloc
@@ -12,6 +12,7 @@ error
 extensions
 getpagesize
 gettext-h
+open
 stdlib
 xalloc
 unistd