diff --git a/src/lib.rs b/src/lib.rs
index ee5803c..81d7e49 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -157,8 +157,7 @@ psm_stack_manipulation! {
                 let (stack_base, allocated_stack_size) = guard.stack_area();
                 debug_assert!(allocated_stack_size >= requested_stack_size);
                 set_stack_limit(Some(stack_base as usize));
-                // TODO should we not pass `allocated_stack_size` here?
-                let panic = psm::on_stack(stack_base, requested_stack_size, move || {
+                let panic = psm::on_stack(stack_base, allocated_stack_size, move || {
                     std::panic::catch_unwind(std::panic::AssertUnwindSafe(callback)).err()
                 });
                 drop(guard);
diff --git a/src/mmap_stack_restore_guard.rs b/src/mmap_stack_restore_guard.rs
index 1e021c2..3a4f3d5 100644
--- a/src/mmap_stack_restore_guard.rs
+++ b/src/mmap_stack_restore_guard.rs
@@ -82,7 +82,7 @@ impl StackRestoreGuard {
         unsafe {
             (
                 self.mapping.add(self.page_size),
-                self.size_with_guard - self.page_size,
+                self.size_with_guard - 2 * self.page_size,
             )
         }
     }
@@ -103,3 +103,20 @@ fn page_size() -> usize {
     // FIXME: consider caching the page size.
     unsafe { libc::sysconf(libc::_SC_PAGE_SIZE) as usize }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_stack_area() {
+        for stack_size_kb in 1..64 {
+            let size = stack_size_kb * 1024;
+            let stack = StackRestoreGuard::new(size);
+            assert_eq!(
+                stack.stack_area().1,
+                ((size + page_size() - 1) / page_size()) * page_size()
+            )
+        }
+    }
+}
\ No newline at end of file