diff --git a/mkspecs/common/windows-vulkan.conf b/mkspecs/common/windows-vulkan.conf
index c928a8f315..5f930c7910 100644
--- a/mkspecs/common/windows-vulkan.conf
+++ b/mkspecs/common/windows-vulkan.conf
@@ -1,5 +1,5 @@
 # Pick up the VULKAN_SDK env var set by the LunarG SDK so that the Vulkan
 # headers are found out-of-the-box on typical Windows setups.
 
-QMAKE_INCDIR_VULKAN     = $(VULKAN_SDK)\\include
+QMAKE_INCDIR_VULKAN     = $$(VULKAN_SDK)\\include
 QMAKE_LIBS_VULKAN       =