diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index 34d7242f8..fd3212332 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,9 @@
+2013-05-21  Corinna Vinschen  <corinna@vinschen.de>
+
+	* globals.cc (__isthreaded): New global variable.  Explain what it's
+	used for.
+	* miscfuncs.cc (thread_wrapper): Set __isthreaded to 1 here.
+
 2013-05-21  Corinna Vinschen  <corinna@vinschen.de>
 
 	* fhandler.h (class fhandler_dev_random): Change type of pseudo to
diff --git a/winsup/cygwin/globals.cc b/winsup/cygwin/globals.cc
index 887326156..9462c7a0c 100644
--- a/winsup/cygwin/globals.cc
+++ b/winsup/cygwin/globals.cc
@@ -75,6 +75,13 @@ bool detect_bloda = false;
 
 bool NO_COPY in_forkee;
 
+/* Taken from BSD libc:
+   This variable is zero until a process has created a pthread.  It is used
+   to avoid calling locking functions in libc when they are not required.
+   Note that this is moderately dangerous.  Do not rely on it if the public
+   API is also used from a non-pthread thread like the signal thread. */
+int NO_COPY __isthreaded = 0;
+
 int __argc_safe;
 int __argc;
 char **__argv;
diff --git a/winsup/cygwin/miscfuncs.cc b/winsup/cygwin/miscfuncs.cc
index 409392760..6a204a01e 100644
--- a/winsup/cygwin/miscfuncs.cc
+++ b/winsup/cygwin/miscfuncs.cc
@@ -473,6 +473,9 @@ thread_wrapper (PVOID arg)
   if (!arg)
     return ERROR_INVALID_PARAMETER;
 
+  /* The process is now threaded.  Note the fact for later usage. */
+  __isthreaded = 1;
+
   /* Fetch thread wrapper info and free from cygheap. */
   thread_wrapper_arg wrapper_arg = *(thread_wrapper_arg *) arg;
   cfree (arg);