diff --git a/ports/esp32/CMakeLists.txt b/ports/esp32/CMakeLists.txt
index a4970c1a1b0b..4e29e9610945 100644
--- a/ports/esp32/CMakeLists.txt
+++ b/ports/esp32/CMakeLists.txt
@@ -47,7 +47,7 @@ set(SDKCONFIG_DEFAULTS ${CMAKE_BINARY_DIR}/sdkconfig.combined)
 include($ENV{IDF_PATH}/tools/cmake/project.cmake)
 
 # Set the location of the main component for the project (one per target).
-set(EXTRA_COMPONENT_DIRS main_${IDF_TARGET})
+list(APPEND EXTRA_COMPONENT_DIRS main_${IDF_TARGET})
 
 # Define the project.
 project(micropython)