diff --git a/as/CMakeLists.txt b/as/CMakeLists.txt
index 70638fe..7a7b6a5 100644
--- a/as/CMakeLists.txt
+++ b/as/CMakeLists.txt
@@ -2,4 +2,15 @@
 
 project(6502 VERSION 0.1.0 LANGUAGES C)
 
+include(TestBigEndian)
+test_big_endian(BIG_ENDIAN)
+
+
+if (${BIG_ENDIAN})
+	add_compile_definitions(BIG_ENDIAN)
+else()
+	add_compile_definitions(LITTLE_ENDIAN)
+endif()
+
+
 add_executable(6502-as main.c as.h as.c map.h map.c hash.c hash.c)