diff --git a/build.rs b/build.rs
index 2cbf54e..ba7fea0 100644
--- a/build.rs
+++ b/build.rs
@@ -23,7 +23,7 @@ fn main() {
 
     let dst = autotools::Config::new(LIB_GC_DIR)
         .cflag(format!(
-            "-I{} -L/lib/x86_64-linux-gnu -lpthread -fPIC",
+            "-I{} -L/lib/x86_64-linux-gnu -lpthread -fPIC -D POINTER_MASK=0x7",
             dst.join("include").display()
         ))
         .build();
@@ -59,7 +59,10 @@ fn main() {
     let dst = Config::new(LIB_GC_DIR)
         .profile("Release")
         .define("BUILD_SHARED_LIBS", "FALSE")
-        .cflag(format!("-I{}", libatomic_include_path))
+        .cflag(format!(
+            "-I{} -DPOINTER_MASK=0x7",
+            libatomic_include_path, foo
+        ))
         .build();
 
     println!(
diff --git a/src/lib.rs b/src/lib.rs
index f84c7cc..e7f0574 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -25,6 +25,7 @@ extern "C" {
     fn GC_get_stack_base(stack_base: *mut GcStackBase) -> c_int;
     fn GC_init();
     fn GC_malloc(size: size_t) -> *mut c_void;
+    fn GC_memalign(align: size_t, size: size_t) -> *mut c_void;
     fn GC_realloc(ptr: *mut c_void, size: size_t) -> *mut c_void;
     fn GC_register_my_thread(stack_base: *const GcStackBase) -> c_int;
     fn GC_set_stackbottom(thread: *const c_void, stack_bottom: *const GcStackBase);
@@ -126,7 +127,7 @@ impl Allocator {
 
 unsafe impl GlobalAlloc for Allocator {
     unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
-        GC_malloc(layout.size()) as *mut u8
+        GC_memalign(layout.align(), layout.size()) as *mut u8
     }
 
     unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {