diff --git a/configure.ac b/configure.ac
index b2c066a2..e8a1650b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -924,6 +924,10 @@ if [ test -n "$DOXYGEN" ]
 fi
 
 
+#---- check for pthreads library
+AC_SEARCH_LIBS([pthread_mutex_init],[pthread],[AC_DEFINE([HAVE_PTHREADS], [1], [Have pthreads library])], [AC_MSG_WARN([pthreads not available])])
+
+
 dnl -----
 dnl ----- Start of "Things needed for gldns" section
 dnl -----
diff --git a/src/compat/arc4_lock.c b/src/compat/arc4_lock.c
index 44662841..facf9575 100644
--- a/src/compat/arc4_lock.c
+++ b/src/compat/arc4_lock.c
@@ -34,6 +34,23 @@
 #include "config.h"
 #define LOCKRET(func) func
 
+#ifdef HAVE_PTHREADS
+#include "pthread.h"
+
+static pthread_mutex_t arc_lock = PTHREAD_MUTEX_INITIALIZER;
+
+void _ARC4_LOCK(void)
+{
+    pthread_mutex_lock(&arc_lock);
+}
+
+void _ARC4_UNLOCK(void)
+{
+    pthread_mutex_unlock(&arc_lock);
+}
+
+#else
+/* XXX - add windows-(or at least non pthread) specific lock routines here */
 void _ARC4_LOCK(void)
 {
 }
@@ -41,4 +58,4 @@ void _ARC4_LOCK(void)
 void _ARC4_UNLOCK(void)
 {
 }
-
+#endif