diff --git a/src/backend.rs b/src/backend.rs
index 8de199f..ed71c91 100644
--- a/src/backend.rs
+++ b/src/backend.rs
@@ -8,8 +8,6 @@ pub trait Backend<T> {
     fn set_ptr(provenance: *mut T, addr: Self) -> Self::Stored;
 
     fn get_int(s: Self::Stored) -> Self;
-
-    fn set_int(s: Self::Stored, int: Self) -> Self::Stored;
 }
 
 impl<T> Backend<T> for usize {
@@ -26,8 +24,44 @@ impl<T> Backend<T> for usize {
     fn get_int(s: Self::Stored) -> Self {
         Strict::addr(s)
     }
+}
 
-    fn set_int(s: Self::Stored, int: Self) -> Self::Stored {
-        Strict::with_addr(s, int)
+#[cfg(target_pointer_width = "64")]
+/// on 64 bit, we can just treat u64/usize interchangeably, because uintptr_t == size_t in Rust
+impl<T> Backend<T> for u64 {
+    type Stored = *mut T;
+
+    fn get_ptr(s: Self::Stored) -> (*mut T, Self) {
+        (s, Strict::addr(s) as u64)
+    }
+
+    fn set_ptr(provenance: *mut T, addr: Self) -> Self::Stored {
+        Strict::with_addr(provenance, addr as usize)
+    }
+
+    fn get_int(s: Self::Stored) -> Self {
+        Strict::addr(s) as u64
+    }
+}
+
+#[cfg(target_pointer_width = "64")]
+impl<T> Backend<T> for u128 {
+    // this one keeps the MSB in the pointer address, and the LSB in the integer
+
+    type Stored = (*mut T, u64);
+
+    fn get_ptr(s: Self::Stored) -> (*mut T, Self) {
+        (s.0, Self::get_int(s))
+    }
+
+    fn set_ptr(provenance: *mut T, addr: Self) -> Self::Stored {
+        let ptr_addr = (addr >> 64) as u64;
+        let int_addr = addr as u64; // truncate it
+        (Strict::with_addr(provenance, ptr_addr as usize), int_addr)
+    }
+
+    fn get_int(s: Self::Stored) -> Self {
+        let ptr_addr = Strict::addr(s.0) as u64;
+        (u128::from(ptr_addr) << 64) | u128::from(s.1)
     }
 }