diff --git a/vulkan/libvulkan/stubhal.cpp b/vulkan/libvulkan/stubhal.cpp
index 2926268..726e854 100644
--- a/vulkan/libvulkan/stubhal.cpp
+++ b/vulkan/libvulkan/stubhal.cpp
@@ -97,7 +97,7 @@
     return VK_SUCCESS;
 }
 
-VKAPI_ATTR PFN_vkVoidFunction GetInstanceProcAddr(VkInstance /*instance*/,
+VKAPI_ATTR PFN_vkVoidFunction GetInstanceProcAddr(VkInstance instance,
                                                   const char* name) {
     if (strcmp(name, "vkCreateInstance") == 0)
         return reinterpret_cast<PFN_vkVoidFunction>(CreateInstance);
@@ -110,7 +110,9 @@
         return reinterpret_cast<PFN_vkVoidFunction>(EnumeratePhysicalDevices);
     if (strcmp(name, "vkGetInstanceProcAddr") == 0)
         return reinterpret_cast<PFN_vkVoidFunction>(GetInstanceProcAddr);
-
+    // Per the spec, return NULL if instance is NULL.
+    if (!instance)
+        return nullptr;
     // None of the other Vulkan functions should ever be called, as they all
     // take a VkPhysicalDevice or other object obtained from a physical device.
     return reinterpret_cast<PFN_vkVoidFunction>(NoOp);