diff --git a/backend/canisters/online_users/impl/src/lifecycle/post_upgrade.rs b/backend/canisters/online_users/impl/src/lifecycle/post_upgrade.rs
index 7ba1c36fda..a434762fb0 100644
--- a/backend/canisters/online_users/impl/src/lifecycle/post_upgrade.rs
+++ b/backend/canisters/online_users/impl/src/lifecycle/post_upgrade.rs
@@ -1,6 +1,6 @@
 use crate::lifecycle::{init_env, init_state};
 use crate::memory::get_upgrades_memory;
-use crate::Data;
+use crate::{mutate_state, Data};
 use canister_logger::LogEntry;
 use canister_tracing_macros::trace;
 use ic_cdk::post_upgrade;
@@ -24,4 +24,7 @@ fn post_upgrade(args: Args) {
     init_state(env, data, args.wasm_version);
 
     info!(version = %args.wasm_version, "Post-upgrade complete");
+
+    // TODO remove this after upgrade
+    mutate_state(|state| state.data.principal_to_user_id_map.clear());
 }
diff --git a/backend/canisters/online_users/impl/src/model/principal_to_user_id_map.rs b/backend/canisters/online_users/impl/src/model/principal_to_user_id_map.rs
index 93ed0cdfb8..d4fb12df1e 100644
--- a/backend/canisters/online_users/impl/src/model/principal_to_user_id_map.rs
+++ b/backend/canisters/online_users/impl/src/model/principal_to_user_id_map.rs
@@ -18,6 +18,10 @@ impl PrincipalToUserIdMap {
     pub fn get(&self, principal: &Principal) -> Option<UserId> {
         self.map.get(principal).map(|u| u.into())
     }
+
+    pub fn clear(&mut self) {
+        self.map.clear_new()
+    }
 }
 
 fn init_map() -> StableBTreeMap<Principal, Principal, Memory> {