diff --git a/ports/gdal/portfile.cmake b/ports/gdal/portfile.cmake
index 84548e3..47abede 100644
--- a/ports/gdal/portfile.cmake
+++ b/ports/gdal/portfile.cmake
@@ -87,12 +87,13 @@ vcpkg_configure_cmake(
         -DGDAL_OGR_FRMTS_POSTGIS=${WITH_POSTGIS}
         -DGDAL_OGR_FRMTS_WFS=${WITH_WFS}
         -DGDAL_OPENCL_SUPPORT=${WITH_OPENCL}
-        -DVCPKG_ALLOW_SYSTEM_LIBS=${VCPKG_ALLOW_SYSTEM_LIBS}
     OPTIONS_RELEASE
         -DGDAL_BUILD_TOOLS=${WITH_TOOLS}
     OPTIONS_DEBUG
         -DGDAL_INSTALL_DATA_FILES=OFF
         -DGDAL_BUILD_TOOLS=OFF
+    MAYBE_UNUSED_VARIABLES
+        -DVCPKG_ALLOW_SYSTEM_LIBS=${VCPKG_ALLOW_SYSTEM_LIBS}
 )
 
 #vcpkg_fixup_pkgconfig_mod()