diff --git a/cmake/QtBuild.cmake b/cmake/QtBuild.cmake
index e04069c648..24245178a5 100644
--- a/cmake/QtBuild.cmake
+++ b/cmake/QtBuild.cmake
@@ -383,7 +383,7 @@ set(QT_PLATFORM_DEFINITION_BUILD_INTERFACE_BASE_DIR
 # Used by qtbase and consumers in non-prefix builds via BUILD_INTERFACE
 if(NOT QT_WILL_INSTALL)
     set(QT_PLATFORM_DEFINITION_BUILD_INTERFACE_BASE_DIR
-        "${CMAKE_BINARY_DIR}/${INSTALL_MKSPECSDIR}"
+        "${QT_BUILD_DIR}/${INSTALL_MKSPECSDIR}"
     )
 endif()