diff --git a/pox-locking/src/lib.rs b/pox-locking/src/lib.rs
index 05303a4d9b..1127e6b667 100644
--- a/pox-locking/src/lib.rs
+++ b/pox-locking/src/lib.rs
@@ -107,6 +107,20 @@ pub fn handle_contract_call_special_cases(
             result,
         );
     } else if *contract_id == boot_code_id(POX_3_NAME, global_context.mainnet) {
+        if !pox_3::is_read_only(function_name) && global_context.epoch_id >= StacksEpochId::Epoch25
+        {
+            warn!("PoX-3 function call attempted on an account after Epoch 2.5";
+                  "v3_unlock_ht" => global_context.database.get_v3_unlock_height(),
+                  "current_burn_ht" => global_context.database.get_current_burnchain_block_height(),
+                  "function_name" => function_name,
+                  "contract_id" => %contract_id
+            );
+            return Err(ClarityError::Runtime(
+                RuntimeErrorType::DefunctPoxContract,
+                None,
+            ));
+        }
+
         return pox_3::handle_contract_call(
             global_context,
             sender,
diff --git a/pox-locking/src/pox_3.rs b/pox-locking/src/pox_3.rs
index 3323a27e34..cdfd0c740c 100644
--- a/pox-locking/src/pox_3.rs
+++ b/pox-locking/src/pox_3.rs
@@ -33,6 +33,33 @@ use crate::{LockingError, POX_3_NAME};
 
 /////////////////////// PoX-3 /////////////////////////////////
 
+/// is a PoX-3 function call read only?
+pub(crate) fn is_read_only(func_name: &str) -> bool {
+    "get-pox-rejection" == func_name
+        || "is-pox-active" == func_name
+        || "burn-height-to-reward-cycle" == func_name
+        || "reward-cycle-to-burn-height" == func_name
+        || "current-pox-reward-cycle" == func_name
+        || "get-stacker-info" == func_name
+        || "get-check-delegation" == func_name
+        || "get-reward-set-size" == func_name
+        || "next-cycle-rejection-votes" == func_name
+        || "get-total-ustx-stacked" == func_name
+        || "get-reward-set-pox-address" == func_name
+        || "get-stacking-minimum" == func_name
+        || "check-pox-addr-version" == func_name
+        || "check-pox-addr-hashbytes" == func_name
+        || "check-pox-lock-period" == func_name
+        || "can-stack-stx" == func_name
+        || "minimal-can-stack-stx" == func_name
+        || "get-pox-info" == func_name
+        || "get-delegation-info" == func_name
+        || "get-allowance-contract-callers" == func_name
+        || "get-num-reward-set-pox-addresses" == func_name
+        || "get-partial-stacked-by-cycle" == func_name
+        || "get-total-pox-rejection" == func_name
+}
+
 /// Lock up STX for PoX for a time.  Does NOT touch the account nonce.
 pub fn pox_lock_v3(
     db: &mut ClarityDatabase,
diff --git a/stackslib/src/chainstate/stacks/boot/pox_4_tests.rs b/stackslib/src/chainstate/stacks/boot/pox_4_tests.rs
index 987ab35a4c..9193fb80f5 100644
--- a/stackslib/src/chainstate/stacks/boot/pox_4_tests.rs
+++ b/stackslib/src/chainstate/stacks/boot/pox_4_tests.rs
@@ -899,8 +899,14 @@ fn pox_3_defunct() {
     );
     burnchain.pox_constants = pox_constants.clone();
 
-    let (mut peer, keys) =
-        instantiate_pox_peer_with_epoch(&burnchain, function_name!(), Some(epochs.clone()), None);
+    let observer = TestEventObserver::new();
+
+    let (mut peer, keys) = instantiate_pox_peer_with_epoch(
+        &burnchain,
+        function_name!(),
+        Some(epochs.clone()),
+        Some(&observer),
+    );
 
     assert_eq!(burnchain.pox_constants.reward_slots(), 6);
     let mut coinbase_nonce = 0;
@@ -949,6 +955,28 @@ fn pox_3_defunct() {
     info!("Submitting stacking txs with pox3");
     latest_block = peer.tenure_with_txs(&txs, &mut coinbase_nonce);
 
+    info!("Checking that stackers have no STX locked");
+    let balances = balances_from_keys(&mut peer, &latest_block, &keys);
+    assert_eq!(balances[0].amount_locked(), 0);
+    assert_eq!(balances[1].amount_locked(), 0);
+
+    info!("Checking tx receipts, all `pox3` calls should have returned `(err ...)`");
+    let last_observer_block = observer
+        .get_blocks()
+        .last()
+        .unwrap()
+        .clone();
+
+    let receipts = last_observer_block.receipts
+        .iter()
+        .filter(|receipt| match &receipt.result {
+            Value::Response(r) => !r.committed,
+            _ => false,
+        })
+        .collect::<Vec<_>>();
+
+    assert_eq!(receipts.len(), 4);
+
     // Advance to start of rewards cycle stackers are participating in
     let target_height = burnchain.pox_constants.pox_4_activation_height + 5;
     while get_tip(peer.sortdb.as_ref()).block_height < u64::from(target_height) {
@@ -985,8 +1013,7 @@ fn pox_3_defunct() {
     }
 }
 
-/// Test that we can lock STX for a couple cycles after pox4 starts,
-/// and that it unlocks after the desired number of cycles
+// Test that STX locked in pox3 automatically unlocks at `v3_unlock_height`
 #[test]
 fn pox_3_unlocks() {
     // Config for this test