diff --git a/contrib/ports/CMakeCommon.cmake b/contrib/ports/CMakeCommon.cmake
index 6465e500..3ef478bb 100644
--- a/contrib/ports/CMakeCommon.cmake
+++ b/contrib/ports/CMakeCommon.cmake
@@ -1,7 +1,10 @@
 set(LWIP_CONTRIB_DIR ${LWIP_DIR}/contrib)
 
 # ARM mbedtls support https://tls.mbed.org/
-set(MBEDTLSDIR ${LWIP_DIR}/../mbedtls)
+if(NOT DEFINED MBEDTLSDIR)
+    message(STATUS "MBEDTLSDIR not set - using default location ${LWIP_DIR}/../mbedtls")
+    set(MBEDTLSDIR ${LWIP_DIR}/../mbedtls)
+endif()
 if(EXISTS ${MBEDTLSDIR}/CMakeLists.txt)
     set(LWIP_HAVE_MBEDTLS ON BOOL)
 
diff --git a/contrib/ports/win32/Filelists.cmake b/contrib/ports/win32/Filelists.cmake
index 03096abb..a6e6b5b5 100644
--- a/contrib/ports/win32/Filelists.cmake
+++ b/contrib/ports/win32/Filelists.cmake
@@ -16,7 +16,10 @@ set(lwipcontribportwindows_SRCS
 )
 
 # pcapif needs WinPcap developer package: https://www.winpcap.org/devel.htm
-set(WPDPACK_DIR ${LWIP_DIR}/../WpdPack)
+if(NOT DEFINED WPDPACK_DIR)
+    message(STATUS "WPDPACK_DIR not set - using default location ${LWIP_DIR}/../WpdPack")
+    set(WPDPACK_DIR ${LWIP_DIR}/../WpdPack)
+endif()
 find_library(WPCAP  wpcap  HINTS ${WPDPACK_DIR}/lib)
 find_library(PACKET packet HINTS ${WPDPACK_DIR}/lib)