-#else
-/* USE_THREADS is not defined */
-#define MUTEX_LOCK(m)
-#define MUTEX_UNLOCK(m)
-#define MUTEX_INIT(m)
-#define MUTEX_DESTROY(m)
-#define COND_INIT(c)
-#define COND_SIGNAL(c)
-#define COND_BROADCAST(c)
-#define COND_WAIT(c, m)
-#define COND_DESTROY(c)
-#define LOCK_SV_MUTEX
-#define UNLOCK_SV_MUTEX
-#define LOCK_STRTAB_MUTEX
-#define UNLOCK_STRTAB_MUTEX
-
-#define THR
-/* Rats: if dTHR is just blank then the subsequent ";" throws an error */
-#ifdef WIN32
-#define dTHR extern int Perl___notused
-#else
-#define dTHR extern int errno
+#ifndef COND_SIGNAL
+# define COND_SIGNAL(c)
+#endif
+
+#ifndef COND_BROADCAST
+# define COND_BROADCAST(c)
+#endif
+
+#ifndef COND_WAIT
+# define COND_WAIT(c, m)
+#endif
+
+#ifndef COND_DESTROY
+# define COND_DESTROY(c)
+#endif
+
+#ifndef LOCK_SV_MUTEX
+# define LOCK_SV_MUTEX
+#endif
+
+#ifndef UNLOCK_SV_MUTEX
+# define UNLOCK_SV_MUTEX
+#endif
+
+#ifndef LOCK_STRTAB_MUTEX
+# define LOCK_STRTAB_MUTEX
+#endif
+
+#ifndef UNLOCK_STRTAB_MUTEX
+# define UNLOCK_STRTAB_MUTEX
+#endif
+
+#ifndef LOCK_CRED_MUTEX
+# define LOCK_CRED_MUTEX
+#endif
+
+#ifndef UNLOCK_CRED_MUTEX
+# define UNLOCK_CRED_MUTEX
+#endif
+
+#ifndef LOCK_FDPID_MUTEX
+# define LOCK_FDPID_MUTEX
+#endif
+
+#ifndef UNLOCK_FDPID_MUTEX
+# define UNLOCK_FDPID_MUTEX
+#endif
+
+#ifndef LOCK_SV_LOCK_MUTEX
+# define LOCK_SV_LOCK_MUTEX
+#endif
+
+#ifndef UNLOCK_SV_LOCK_MUTEX
+# define UNLOCK_SV_LOCK_MUTEX
+#endif
+
+#ifndef LOCK_DOLLARZERO_MUTEX
+# define LOCK_DOLLARZERO_MUTEX
+#endif
+
+#ifndef UNLOCK_DOLLARZERO_MUTEX
+# define UNLOCK_DOLLARZERO_MUTEX
+#endif
+
+/* THR, SET_THR, and dTHR are there for compatibility with old versions */
+#ifndef THR
+# define THR PERL_GET_THX
+#endif
+
+#ifndef SET_THR
+# define SET_THR(t) PERL_SET_THX(t)
+#endif
+
+#ifndef dTHR
+# define dTHR dNOOP
+#endif
+
+#ifndef INIT_THREADS
+# define INIT_THREADS NOOP