diff --git a/modules/lua/lua_vmprep.h b/modules/lua/lua_vmprep.h
index e9d101f7db..374c62b37a 100644
--- a/modules/lua/lua_vmprep.h
+++ b/modules/lua/lua_vmprep.h
@@ -130,6 +130,13 @@ AP_LUA_DECLARE(void) ap_lua_load_apache2_lmodule(lua_State *L);
 AP_LUA_DECLARE(lua_State*) ap_lua_get_lua_state(apr_pool_t *lifecycle_pool,
                                                 ap_lua_vm_spec *spec, request_rec* r);
 
-
+#if APR_HAS_THREADS || defined(DOXYGEN)
+/*
+ * Initialize mod_lua mutex.
+ * @pool pool for mutex
+ * @s server_rec for logging
+ */
+void ap_lua_init_mutex(apr_pool_t *pool, server_rec *s);
+#endif
 
 #endif
diff --git a/modules/lua/mod_lua.c b/modules/lua/mod_lua.c
index f72c1dd0aa..dab098cbe6 100644
--- a/modules/lua/mod_lua.c
+++ b/modules/lua/mod_lua.c
@@ -127,10 +127,6 @@ static void ap_lua_release_state(lua_State* L, ap_lua_vm_spec* spec, request_rec
     }
 }
 
-#if APR_HAS_THREADS
-extern void ap_lua_init_mutex(apr_pool_t *pool, server_rec *s);
-#endif
-
 static ap_lua_vm_spec *create_vm_spec(apr_pool_t **lifecycle_pool,
                                       request_rec *r,
                                       const ap_lua_dir_cfg *cfg,