diff --git a/Makefile b/Makefile
index 89574e9..963ecf0 100644
--- a/Makefile
+++ b/Makefile
@@ -2,6 +2,8 @@ all: test
 
 CC?=clang
 LD?=wasm-ld
+AR?=llvm-ar
+RANLIB?=llvm-ranlib
 JS?=node
 
 .PHONY: test
@@ -15,6 +17,10 @@ test: test.js test.wasm
 test.wasm: test.o walloc.o
 	$(LD) --no-entry --import-memory -o $@ $^
 
+libwalloc.a: walloc.o
+	$(AR) rc $@ $<
+	$(RANLIB) $@
+
 .PHONY: clean
 clean:
-	rm -f *.o *.wasm
+	rm -f *.o *.a *.wasm
diff --git a/walloc.c b/walloc.c
index 1f12357..5760c0e 100644
--- a/walloc.c
+++ b/walloc.c
@@ -38,9 +38,13 @@ typedef __UINT8_TYPE__ uint8_t;
 static inline size_t max(size_t a, size_t b) {
   return a < b ? b : a;
 }
+#if __has_constexpr_builtin(__builtin_align_up)
+#define align __builtin_align_up
+#else
 static inline uintptr_t align(uintptr_t val, uintptr_t alignment) {
   return (val + alignment - 1) & ~(alignment - 1);
 }
+#endif
 #define ASSERT_ALIGNED(x, y) ASSERT((x) == align((x), y))
 
 #define CHUNK_SIZE 256