diff --git a/heed/src/txn.rs b/heed/src/txn.rs
index 242c424c..a6f479d9 100644
--- a/heed/src/txn.rs
+++ b/heed/src/txn.rs
@@ -141,6 +141,15 @@ impl<'a> Deref for RoTxn<'a, WithTls> {
     }
 }
 
+#[cfg(master3)]
+impl<'a> std::ops::DerefMut for RoTxn<'a, WithTls> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        // SAFETY: OK because repr(transparent) means RoTxn<T> always has the same layout
+        // as RoTxnInner.
+        unsafe { std::mem::transmute(self) }
+    }
+}
+
 impl<'a> Deref for RoTxn<'a, WithoutTls> {
     type Target = RoTxn<'a, AnyTls>;
 
@@ -151,6 +160,15 @@ impl<'a> Deref for RoTxn<'a, WithoutTls> {
     }
 }
 
+#[cfg(master3)]
+impl<'a> std::ops::DerefMut for RoTxn<'a, WithoutTls> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        // SAFETY: OK because repr(transparent) means RoTxn<T> always has the same layout
+        // as RoTxnInner.
+        unsafe { std::mem::transmute(self) }
+    }
+}
+
 impl<T> Drop for RoTxn<'_, T> {
     fn drop(&mut self) {
         if let Some(mut txn) = self.inner.txn.take() {