diff --git a/runtime/Makefile b/runtime/Makefile
index aae1c0c0d..210a1ee0e 100644
--- a/runtime/Makefile
+++ b/runtime/Makefile
@@ -1,5 +1,5 @@
 CC=clang
-COMMON_FLAGS=-g2 -std=gnu99 -fstack-protector-all -Wno-error=implicit-function-declaration -arch X86_64
+COMMON_FLAGS=-g2 -std=gnu99 -fstack-protector-all -Wno-error=implicit-function-declaration -arch x86_64
 PROD_FLAGS=$(COMMON_FLAGS) -DLAMA_ENV
 TEST_FLAGS=$(COMMON_FLAGS) -DDEBUG_VERSION
 UNIT_TESTS_FLAGS=$(TEST_FLAGS)
diff --git a/src/X86.ml b/src/X86.ml
index 3bc142ab2..4986327c2 100644
--- a/src/X86.ml
+++ b/src/X86.ml
@@ -1350,7 +1350,7 @@ let build cmd prog =
   cmd#dump_file "i" (Interface.gen prog);
   let inc = get_std_path () in
   let compiler = "clang" in
-  let flags = "-pie -arch X86_64" in
+  let flags = "-pie -arch x86_64" in
   match cmd#get_mode with
   | `Default ->
       let objs = find_objects (fst @@ fst prog) cmd#get_include_paths in