diff --git a/src/platforms/posix/px4_layer/drv_hrt.c b/src/platforms/posix/px4_layer/drv_hrt.c
index 48587c7d93..7af4431b9c 100644
--- a/src/platforms/posix/px4_layer/drv_hrt.c
+++ b/src/platforms/posix/px4_layer/drv_hrt.c
@@ -299,7 +299,7 @@ void	hrt_stop_delay()
 	_start_delay_time = 0;
 
 	if (delta > 10000) {
-		PX4_INFO("simulator is slow. Delay added: %llu us", delta);
+		PX4_INFO("simulator is slow. Delay added: %" PRIi64 " us", delta);
 	}
 
 	pthread_mutex_unlock(&_hrt_mutex);
diff --git a/unittests/CMakeLists.txt b/unittests/CMakeLists.txt
index 36f132eec7..43ff39a0d4 100644
--- a/unittests/CMakeLists.txt
+++ b/unittests/CMakeLists.txt
@@ -26,9 +26,9 @@ include(CheckCXXCompilerFlag)
 CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
 CHECK_CXX_COMPILER_FLAG("-std=c++0x" COMPILER_SUPPORTS_CXX0X)
 if(COMPILER_SUPPORTS_CXX11)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -fno-exceptions -fno-rtti -fno-threadsafe-statics -D__CUSTOM_FILE_IO__ -D__PX4_UNIT_TESTS -g -Wall")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -fno-exceptions -fno-rtti -fno-threadsafe-statics -D__CUSTOM_FILE_IO__ -D__PX4_UNIT_TESTS -g -Wall -Werror")
 elseif(COMPILER_SUPPORTS_CXX0X)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x -fno-exceptions -fno-rtti -fno-threadsafe-statics -D__CUSTOM_FILE_IO__ -D__PX4_UNIT_TESTS -g -Wall")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x -fno-exceptions -fno-rtti -fno-threadsafe-statics -D__CUSTOM_FILE_IO__ -D__PX4_UNIT_TESTS -g -Wall -Werror")
 else()
   message(STATUS "The compiler ${CMAKE_CXX_COMPILER} has no C++11 support. Please use a different C++ compiler.")
 endif()