diff --git a/stm-firmware/CMakeLists.txt b/stm-firmware/CMakeLists.txt
index 614812d..caddc9f 100644
--- a/stm-firmware/CMakeLists.txt
+++ b/stm-firmware/CMakeLists.txt
@@ -56,9 +56,10 @@ add_link_options(-Wl,--gc-sections)
 ENDIF(CMAKE_BUILD_TYPE STREQUAL "Debug")
 
 
-if (DEFINED UART_ON_DEBUG_HEADER)
+if (DEFINED ENV{UART_ON_DEBUG_HEADER})
     add_definitions(-DUART_ON_DEBUG_HEADER)
-endif (DEFINED UART_ON_DEBUG_HEADER)
+    message("UART forced to debug header")
+endif (DEFINED ENV{UART_ON_DEBUG_HEADER})
 
 add_subdirectory(base64-lib)