diff --git a/cmake-nRF5x/CMake_nRF5x.cmake b/cmake-nRF5x/CMake_nRF5x.cmake
index e2b3c068..29273e66 100755
--- a/cmake-nRF5x/CMake_nRF5x.cmake
+++ b/cmake-nRF5x/CMake_nRF5x.cmake
@@ -88,7 +88,7 @@ macro(nRF5x_setup)
         set(SOFTDEVICE_PATH "${NRF5_SDK_PATH}/components/softdevice/s132/hex/s132_nrf52_6.1.1_softdevice.hex")
     endif ()
 
-    set(COMMON_FLAGS "-MP -MD -mthumb -mabi=aapcs -Wall -g3 -ffunction-sections -fdata-sections -fno-strict-aliasing -fno-builtin --short-enums ${CPU_FLAGS}")
+    set(COMMON_FLAGS "-MP -MD -mthumb -mabi=aapcs -Wall -g3 -ffunction-sections -fdata-sections -fno-strict-aliasing -fno-builtin --short-enums ${CPU_FLAGS} -Wreturn-type -Werror=return-type")
 
     # compiler/assambler/linker flags
     set(CMAKE_C_FLAGS "${COMMON_FLAGS}")
diff --git a/src/DisplayApp/DisplayApp.cpp b/src/DisplayApp/DisplayApp.cpp
index 9da2d7ed..36302a20 100644
--- a/src/DisplayApp/DisplayApp.cpp
+++ b/src/DisplayApp/DisplayApp.cpp
@@ -9,7 +9,7 @@ using namespace Pinetime::Applications;
 
 Pinetime::Drivers::st7789 lcd;
 ret_code_t lcd_init() {
-  lcd.Init();
+  return lcd.Init();
 }
 
 void lcd_dummy() {
@@ -38,7 +38,7 @@ static lcd_cb_t st7789_cb = {
         .width = 240
 };
 
-const nrf_lcd_t nrf_lcd_st7789 = {
+static const nrf_lcd_t nrf_lcd_st7789 = {
         .lcd_init = lcd_init,
         .lcd_uninit = lcd_dummy,
         .lcd_pixel_draw = lcd_pixel_draw,
@@ -64,7 +64,7 @@ void DisplayApp::Process(void *instance) {
   auto* app = static_cast<DisplayApp*>(instance);
 
   NRF_LOG_INFO("DisplayApp task started!");
-  gfx_initialization();
+  app->gfx_initialization();
   uint8_t hour = 0;
   uint8_t minute = 1;
   while (1) {
diff --git a/src/DisplayApp/DisplayApp.h b/src/DisplayApp/DisplayApp.h
index 97d4d18b..08ecedef 100644
--- a/src/DisplayApp/DisplayApp.h
+++ b/src/DisplayApp/DisplayApp.h
@@ -11,7 +11,7 @@ namespace Pinetime {
       private:
         TaskHandle_t taskHandle;
         static void Process(void* instance);
-        static void gfx_initialization();
+        void gfx_initialization();
 
     };
   }
diff --git a/src/drivers/spi_master_fast.h b/src/drivers/spi_master_fast.h
index 5cd4d7ae..3cda6ea6 100644
--- a/src/drivers/spi_master_fast.h
+++ b/src/drivers/spi_master_fast.h
@@ -78,7 +78,7 @@ typedef struct
             uint8_t mode : 2;       /*!< SPI master mode */
             uint8_t : 5;            /*!< Padding */
         }fields;
-    }config;    
+    }config;
     uint8_t frequency;              /*!< SPI master frequency */
     uint8_t pin_SCK;                /*!< SPI master SCK pin */
     uint8_t pin_MOSI;               /*!< SPI master MOSI pin */
@@ -143,5 +143,5 @@ bool spi_master_tx(SPI_module_number_t spi_num, uint16_t transfer_size, const ui
  * @retval false if transmit/reveive of transfer_size were not complete and tx_data/rx_data points to invalid data.
  */
 bool spi_master_rx(SPI_module_number_t spi_num, uint16_t transfer_size, uint8_t *rx_data);
- 
+
 #endif
diff --git a/src/drivers/st7789.cpp b/src/drivers/st7789.cpp
index a4d06266..e88f110a 100644
--- a/src/drivers/st7789.cpp
+++ b/src/drivers/st7789.cpp
@@ -8,7 +8,7 @@ using namespace Pinetime::Drivers;
 ret_code_t st7789::Init() {
   InitHw();
   InitCommands();
-
+  return 0;
 }
 
 ret_code_t st7789::InitHw() const {