diff --git a/ports/esp32/main/CMakeLists.txt b/ports/esp32/main/CMakeLists.txt
index 1cc30b71ec..d01656e567 100644
--- a/ports/esp32/main/CMakeLists.txt
+++ b/ports/esp32/main/CMakeLists.txt
@@ -1,5 +1,7 @@
 # Set location of base MicroPython directory.
-get_filename_component(MICROPY_DIR ${PROJECT_DIR}/../.. ABSOLUTE)
+if(NOT MICROPY_DIR)
+    get_filename_component(MICROPY_DIR ${PROJECT_DIR}/../.. ABSOLUTE)
+endif()
 
 # Include core source components.
 include(${MICROPY_DIR}/py/py.cmake)