diff --git a/src/scheduler/worker.rs b/src/scheduler/worker.rs
index cc1b28e23b..40a54e4046 100644
--- a/src/scheduler/worker.rs
+++ b/src/scheduler/worker.rs
@@ -71,15 +71,17 @@ impl<VM: VMBinding> GCWorkerShared<VM> {
         let bytes = VM::VMObjectModel::get_current_size(object);
         // Get the space index from descriptor
         let space_descriptor = VM_MAP.get_descriptor_for_address(object.to_raw_address());
-        let space_index = space_descriptor.get_index();
-        debug_assert!(
-            space_index < MAX_SPACES,
-            "Space index {} is not in the range of [0, {})",
-            space_index,
-            MAX_SPACES
-        );
-        // Accumulate the live bytes for the index
-        live_bytes_per_space[space_index] += bytes;
+        if space_descriptor != crate::util::heap::space_descriptor::SpaceDescriptor::UNINITIALIZED {
+            let space_index = space_descriptor.get_index();
+            debug_assert!(
+                space_index < MAX_SPACES,
+                "Space index {} is not in the range of [0, {})",
+                space_index,
+                MAX_SPACES
+            );
+            // Accumulate the live bytes for the index
+            live_bytes_per_space[space_index] += bytes;
+        }
     }
 }
 
diff --git a/src/util/heap/layout/map.rs b/src/util/heap/layout/map.rs
index afb336cf61..ccb46be19b 100644
--- a/src/util/heap/layout/map.rs
+++ b/src/util/heap/layout/map.rs
@@ -81,6 +81,8 @@ pub trait VMMap: Sync {
 
     fn is_finalized(&self) -> bool;
 
+    /// Get the space descriptor for the given address. Return SpaceDescriptor::UNINITIALIZED if the
+    /// address is not within the MMTk heap range, or not within MMTk spaces.
     fn get_descriptor_for_address(&self, address: Address) -> SpaceDescriptor;
 
     fn add_to_cumulative_committed_pages(&self, pages: usize);
diff --git a/src/util/heap/layout/map32.rs b/src/util/heap/layout/map32.rs
index cf209f1186..67a27d7a51 100644
--- a/src/util/heap/layout/map32.rs
+++ b/src/util/heap/layout/map32.rs
@@ -255,7 +255,10 @@ impl VMMap for Map32 {
 
     fn get_descriptor_for_address(&self, address: Address) -> SpaceDescriptor {
         let index = address.chunk_index();
-        self.descriptor_map[index]
+        self.descriptor_map
+            .get(index)
+            .copied()
+            .unwrap_or(SpaceDescriptor::UNINITIALIZED)
     }
 
     fn add_to_cumulative_committed_pages(&self, pages: usize) {
diff --git a/src/util/heap/layout/map64.rs b/src/util/heap/layout/map64.rs
index 08de2cde37..609cd05c7c 100644
--- a/src/util/heap/layout/map64.rs
+++ b/src/util/heap/layout/map64.rs
@@ -206,8 +206,11 @@ impl VMMap for Map64 {
     }
 
     fn get_descriptor_for_address(&self, address: Address) -> SpaceDescriptor {
-        let index = Self::space_index(address).unwrap();
-        self.inner().descriptor_map[index]
+        if let Some(index) = Self::space_index(address) {
+            self.inner().descriptor_map[index]
+        } else {
+            SpaceDescriptor::UNINITIALIZED
+        }
     }
 
     fn add_to_cumulative_committed_pages(&self, pages: usize) {