diff --git a/src/simplevk.cpp b/src/simplevk.cpp
index 70dcb306792..583b8b0bde4 100644
--- a/src/simplevk.cpp
+++ b/src/simplevk.cpp
@@ -63,15 +63,19 @@ PFN_vkGetInstanceProcAddr vkGetInstanceProcAddr = 0;
 
 int load_vulkan_driver(const char* /*driver_path*/)
 {
-    ncnn::vkEnumerateInstanceExtensionProperties = ::vkEnumerateInstanceExtensionProperties;
-    ncnn::vkCreateInstance = ::vkCreateInstance;
-    ncnn::vkGetInstanceProcAddr = ::vkGetInstanceProcAddr;
+    vkEnumerateInstanceExtensionProperties = ::vkEnumerateInstanceExtensionProperties;
+    vkCreateInstance = ::vkCreateInstance;
+    vkGetInstanceProcAddr = ::vkGetInstanceProcAddr;
 
     return 0;
 }
 
 int unload_vulkan_driver()
 {
+    vkEnumerateInstanceExtensionProperties = 0;
+    vkCreateInstance = 0;
+    vkGetInstanceProcAddr = 0;
+
     return 0;
 }
 
@@ -629,6 +633,10 @@ int load_vulkan_driver(const char* driver_path)
 
 int unload_vulkan_driver()
 {
+    vkEnumerateInstanceExtensionProperties = 0;
+    vkCreateInstance = 0;
+    vkGetInstanceProcAddr = 0;
+
 #if defined _WIN32
     if (g_libvulkan)
     {
diff --git a/src/simplevk.h b/src/simplevk.h
index 84d6a5fff42..6b0ad8c7689 100644
--- a/src/simplevk.h
+++ b/src/simplevk.h
@@ -2187,8 +2187,13 @@ extern PFN_vkEnumerateInstanceExtensionProperties vkEnumerateInstanceExtensionPr
 extern PFN_vkCreateInstance vkCreateInstance;
 extern PFN_vkGetInstanceProcAddr vkGetInstanceProcAddr;
 
-int load_vulkan_driver(const char* driver_path);
+// Load vulkan driver dynamic library when driver_path is provided
+// Load from env VK_ICD_FILENAMES and NCNN_VULKAN_DRIVER otherwise
+// If failed, it will try system libvulkan and well-known library names
+// The three vulkan base function pointers will be set on success
+int load_vulkan_driver(const char* driver_path = 0);
 
+// Unload vulkan driver library and clear
 int unload_vulkan_driver();
 
 } // namespace ncnn