diff --git a/README.md b/README.md
index e728969d..42efda20 100644
--- a/README.md
+++ b/README.md
@@ -102,6 +102,14 @@ $ cd build
 $ cmake -DARM_NONE_EABI_TOOLCHAIN_PATH=... -DNRF5_SDK_PATH=... -DUSE_OPENOCD=1 -DGDB_CLIENT_BIN_PATH=[optional] ../
 ```
 
+
+**Note** : By default, the build configuration *Release* is applied. It means that the code is built with optimisations enabled (-O3). If you wanto to compile in *Debug* mode to ease debugging and step-by-step debugging, specify the CMake variable `CMAKE_BUILD_TYPE` in the CMake command line:
+
+```
+-DCMAKE_BUILD_TYPE=Debug
+```
+ 
+
   * Make
 ```
 $ make -j pinetime-app
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 286a792a..1609196a 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -546,6 +546,10 @@ add_definitions(-DNRF52 -DNRF52832 -DNRF52832_XXAA -DNRF52_PAN_74 -DNRF52_PAN_64
 add_definitions(-DFREERTOS)
 add_definitions(-DDEBUG_NRF_USER)
 
+if(NOT CMAKE_BUILD_TYPE)
+  set(CMAKE_BUILD_TYPE "Release")
+endif()
+
 # Build autonomous binary (without support for bootloader)
 set(EXECUTABLE_NAME "pinetime-app")
 set(NRF5_LINKER_SCRIPT "${CMAKE_SOURCE_DIR}/gcc_nrf52.ld")