diff --git a/modules/module-postgres/src/api/PostgresRouteAPIAdapter.ts b/modules/module-postgres/src/api/PostgresRouteAPIAdapter.ts
index 320f1b2b6..19a8acb9e 100644
--- a/modules/module-postgres/src/api/PostgresRouteAPIAdapter.ts
+++ b/modules/module-postgres/src/api/PostgresRouteAPIAdapter.ts
@@ -252,6 +252,10 @@ FROM pg_replication_slots WHERE slot_name = $1 LIMIT 1;`,
 
     const r = await callback(currentLsn);
 
+    // Note: This may not reliably trigger a new replication message on Postgres 11 or 12,
+    // in which case there could be a delay in the client receiving the write checkpoint acknowledgement.
+    // Postgres 12 already reached EOL, and this is not a critical issue, so we're not fixing it.
+    // On postgres 13+, this works reliably.
     await lib_postgres.retriedQuery(this.pool, KEEPALIVE_STATEMENT);
 
     return r;
diff --git a/modules/module-postgres/test/src/checkpoints.test.ts b/modules/module-postgres/test/src/checkpoints.test.ts
index 844e2ee89..7ad247ea1 100644
--- a/modules/module-postgres/test/src/checkpoints.test.ts
+++ b/modules/module-postgres/test/src/checkpoints.test.ts
@@ -12,7 +12,7 @@ const BASIC_SYNC_RULES = `bucket_definitions:
     data:
       - SELECT id, description, other FROM "test_data"`;
 
-describe.skipIf(!(env.CI || env.SLOW_TESTS))('checkpoint tests', () => {
+describe('checkpoint tests', () => {
   test('write checkpoints', { timeout: 50_000 }, async () => {
     const factory = INITIALIZED_MONGO_STORAGE_FACTORY;
     await using context = await WalStreamTestContext.open(factory);
@@ -20,6 +20,14 @@ describe.skipIf(!(env.CI || env.SLOW_TESTS))('checkpoint tests', () => {
     await context.updateSyncRules(BASIC_SYNC_RULES);
     const { pool } = context;
     const api = new PostgresRouteAPIAdapter(pool);
+    const serverVersion = await context.connectionManager.getServerVersion();
+    if (serverVersion!.compareMain('13.0.0') < 0) {
+      // The test is not stable on Postgres 11 or 12. See the notes on
+      // PostgresRouteAPIAdapter.createReplicationHead() for details.
+      // Postgres 12 is already EOL, so not worth finding a fix - just skip the tests.
+      console.log('Skipping write checkpoint test on Postgres < 13.0.0');
+      return;
+    }
 
     await pool.query(`CREATE TABLE test_data(id text primary key, description text, other text)`);
 
@@ -59,7 +67,7 @@ describe.skipIf(!(env.CI || env.SLOW_TESTS))('checkpoint tests', () => {
 
         const start = Date.now();
         while (lastWriteCheckpoint == null || lastWriteCheckpoint < BigInt(cp.writeCheckpoint)) {
-          if (Date.now() - start > 5_000) {
+          if (Date.now() - start > 3_000) {
             throw new Error(
               `Timeout while waiting for checkpoint. last: ${lastWriteCheckpoint}, waiting for: ${cp.writeCheckpoint}`
             );
diff --git a/packages/service-core-tests/src/tests/register-sync-tests.ts b/packages/service-core-tests/src/tests/register-sync-tests.ts
index b9b5d965e..6bf9a2f5e 100644
--- a/packages/service-core-tests/src/tests/register-sync-tests.ts
+++ b/packages/service-core-tests/src/tests/register-sync-tests.ts
@@ -520,8 +520,11 @@ bucket_definitions:
               await batch.commit('0/2');
             });
 
-            // pause for a bit to give the stream time to interrupt the checkpoint
-            await timers.setTimeout(500);
+            if (sentRows >= 1000 && sentRows <= 2001) {
+              // pause for a bit to give the stream time to process interruptions.
+              // This covers the data batch above and the next one.
+              await timers.setTimeout(50);
+            }
           }
         }
         if ('checkpoint_complete' in next) {