diff --git a/cmake/modules/AddCompilerFlags.cmake b/cmake/modules/AddCompilerFlags.cmake
--- a/cmake/modules/AddCompilerFlags.cmake
+++ b/cmake/modules/AddCompilerFlags.cmake
@@ -11,12 +11,19 @@
 	string(APPEND ${TEST_NAME} "_is_supported")
 endmacro()
 
+macro(append_flag_to_variable TARGET_VAR FLAG)
+	if(NOT "${${TARGET_VAR}}" STREQUAL "")
+		string(APPEND ${TARGET_VAR} " ")
+	endif()
+	string(APPEND ${TARGET_VAR} "${FLAG}")
+endmacro()
+
 function(add_c_compiler_flag)
 	foreach(f ${ARGN})
 		build_test_name_from_flag(FLAG_IS_SUPPORTED ${f})
 		CHECK_C_COMPILER_FLAG(${f} ${FLAG_IS_SUPPORTED})
 		if(${FLAG_IS_SUPPORTED})
-			string(APPEND CMAKE_C_FLAGS " ${f}")
+			append_flag_to_variable(CMAKE_C_FLAGS ${f})
 		endif()
 	endforeach()
 	set(CMAKE_C_FLAGS ${CMAKE_C_FLAGS} PARENT_SCOPE)
@@ -27,7 +34,7 @@
 		build_test_name_from_flag(FLAG_IS_SUPPORTED ${f})
 		CHECK_CXX_COMPILER_FLAG(${f} ${FLAG_IS_SUPPORTED})
 		if(${FLAG_IS_SUPPORTED})
-			string(APPEND CMAKE_CXX_FLAGS " ${f}")
+			append_flag_to_variable(CMAKE_CXX_FLAGS ${f})
 		endif()
 	endforeach()
 	set(CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS} PARENT_SCOPE)
@@ -60,7 +67,7 @@
 # (eventually with a warning).
 function(add_linker_flag)
 	foreach(f ${ARGN})
-		string(APPEND CMAKE_EXE_LINKER_FLAGS " ${f}")
+		append_flag_to_variable(CMAKE_EXE_LINKER_FLAGS ${f})
 	endforeach()
 	set(CMAKE_EXE_LINKER_FLAGS ${CMAKE_EXE_LINKER_FLAGS} PARENT_SCOPE)
 endfunction()