diff --git a/extmod/extmod.cmake b/extmod/extmod.cmake
index 954bfc7e96..2207a951ad 100644
--- a/extmod/extmod.cmake
+++ b/extmod/extmod.cmake
@@ -187,8 +187,12 @@ if(MICROPY_SSL_MBEDTLS)
         ${MICROPY_LIB_MBEDTLS_DIR}/library/xtea.c
     )
 
+    if(NOT MBEDTLS_CONFIG_FILE)
+        set(MBEDTLS_CONFIG_FILE "${MICROPY_PORT_DIR}/mbedtls/mbedtls_config.h")
+    endif()
+
     target_compile_definitions(micropy_lib_mbedtls INTERFACE
-        MBEDTLS_CONFIG_FILE="${MICROPY_PORT_DIR}/mbedtls/mbedtls_config.h"
+        MBEDTLS_CONFIG_FILE="${MBEDTLS_CONFIG_FILE}"
     )
 
     list(APPEND MICROPY_INC_CORE