diff --git a/src/ram.rs b/src/ram.rs
index 1d932e11..e03e52ad 100644
--- a/src/ram.rs
+++ b/src/ram.rs
@@ -1,36 +1,35 @@
-use core::cell::RefCell;
 use core::alloc::GlobalAlloc;
 use core::ptr::NonNull;
 use alloc::alloc::Layout;
 use linked_list_allocator::Heap;
+use crate::cortex_a9::mutex::Mutex;
 use crate::zynq::ddr::DdrRam;
 
 #[global_allocator]
-static ALLOCATOR: HeapAlloc = HeapAlloc(RefCell::new(Heap::empty()));
+static ALLOCATOR: CortexA9Alloc = CortexA9Alloc(Mutex::new(Heap::empty()));
 
 /// LockedHeap doesn't locking properly
-struct HeapAlloc(RefCell<Heap>);
+struct CortexA9Alloc(Mutex<Heap>);
 
-/// FIXME: unsound; lock properly
-unsafe impl Sync for HeapAlloc {}
+unsafe impl Sync for CortexA9Alloc {}
 
-unsafe impl GlobalAlloc for HeapAlloc {
+unsafe impl GlobalAlloc for CortexA9Alloc {
     unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
-        self.0.borrow_mut()
+        self.0.lock()
             .allocate_first_fit(layout)
             .ok()
             .map_or(0 as *mut u8, |allocation| allocation.as_ptr())
     }
 
     unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
-        self.0.borrow_mut()
+        self.0.lock()
             .deallocate(NonNull::new_unchecked(ptr), layout)
     }
 }
 
 pub fn init_alloc(ddr: &mut DdrRam) {
     unsafe {
-        ALLOCATOR.0.borrow_mut()
+        ALLOCATOR.0.lock()
             .init(ddr.ptr::<u8>() as usize, ddr.size());
     }
 }