diff --git a/components/hashglobe/src/diagnostic.rs b/components/hashglobe/src/diagnostic.rs
index 0c4df266b34..668a36f7ad2 100644
--- a/components/hashglobe/src/diagnostic.rs
+++ b/components/hashglobe/src/diagnostic.rs
@@ -1,6 +1,7 @@
 use hash_map::HashMap;
 use std::borrow::Borrow;
 use std::hash::{BuildHasher, Hash};
+use std::ptr;
 
 use FailedAllocationError;
 
@@ -9,6 +10,11 @@ const CANARY: usize = 0x42cafe99;
 #[cfg(target_pointer_width = "64")]
 const CANARY: usize = 0x42cafe9942cafe99;
 
+#[cfg(target_pointer_width = "32")]
+const POISON: usize = 0xdeadbeef;
+#[cfg(target_pointer_width = "64")]
+const POISON: usize = 0xdeadbeefdeadbeef;
+
 #[derive(Clone, Debug)]
 enum JournalEntry {
     Insert(usize),
@@ -130,6 +136,9 @@ impl<K: Hash + Eq, V, S: BuildHasher> DiagnosticHashMap<K, V, S>
     {
         assert!(!self.readonly);
         self.journal.push(JournalEntry::Remove(self.map.make_hash(k).inspect()));
+        if let Some(v) = self.map.get_mut(k) {
+            unsafe { ptr::write_volatile(&mut v.0, POISON); }
+        }
         self.map.remove(k).map(|x| x.1)
     }