diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 09ce26d47..ce3a4a8fd 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -21,6 +21,7 @@ set(CMAKE_BUILD_TYPE "${CMAKE_BUILD_TYPE}" CACHE STRING
 	FORCE
 )
 
+set(CMAKE_C_FLAGS "${CMAKE_CFLAGS}  $ENV{CFLAGS} $ENV{CPPFLAGS}")
 
 # Set some random things default to not being visible in the GUI
 mark_as_advanced(EXECUTABLE_OUTPUT_PATH LIBRARY_OUTPUT_PATH)
@@ -746,7 +747,7 @@ else()
 	# - we don't deal with Inf/NaN or signed zero
 	set(MATH_FLAGS "-fno-math-errno -fno-trapping-math -ffinite-math-only -fno-signed-zeros")
 
-	set(CMAKE_CXX_FLAGS_RELEASE "-DNDEBUG ${RELEASE_WARNING_FLAGS} ${WARNING_FLAGS} ${OTHER_FLAGS} -Wall -pipe -funroll-loops")
+	set(CMAKE_CXX_FLAGS_RELEASE "-DNDEBUG ${RELEASE_WARNING_FLAGS} ${WARNING_FLAGS} ${OTHER_FLAGS} -Wall -pipe -funroll-loops $ENV{CPPFLAGS}")
 	if(CMAKE_SYSTEM_NAME MATCHES "(Darwin|BSD|DragonFly)")
 		set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -Os")
 	else()