diff --git a/control_plane/attachment_service/src/service.rs b/control_plane/attachment_service/src/service.rs
index aa930014b2..925910253b 100644
--- a/control_plane/attachment_service/src/service.rs
+++ b/control_plane/attachment_service/src/service.rs
@@ -1523,6 +1523,8 @@ impl Service {
         &self,
         create_req: TenantCreateRequest,
     ) -> Result<TenantCreateResponse, ApiError> {
+        let tenant_id = create_req.new_tenant_id.tenant_id;
+
         // Exclude any concurrent attempts to create/access the same tenant ID
         let _tenant_lock = self
             .tenant_op_locks
@@ -1531,7 +1533,12 @@ impl Service {
 
         let (response, waiters) = self.do_tenant_create(create_req).await?;
 
-        self.await_waiters(waiters, SHORT_RECONCILE_TIMEOUT).await?;
+        if let Err(e) = self.await_waiters(waiters, SHORT_RECONCILE_TIMEOUT).await {
+            // Avoid deadlock: reconcile may fail while notifying compute, if the cloud control plane refuses to
+            // accept compute notifications while it is in the process of creating.  Reconciliation will
+            // be retried in the background.
+            tracing::warn!(%tenant_id, "Reconcile not done yet while creating tenant ({e})");
+        }
         Ok(response)
     }
 
@@ -1610,13 +1617,25 @@ impl Service {
                 splitting: SplitState::default(),
             })
             .collect();
-        self.persistence
+
+        match self
+            .persistence
             .insert_tenant_shards(persist_tenant_shards)
             .await
-            .map_err(|e| {
-                // TODO: distinguish primary key constraint (idempotent, OK), from other errors
-                ApiError::InternalServerError(anyhow::anyhow!(e))
-            })?;
+        {
+            Ok(_) => {}
+            Err(DatabaseError::Query(diesel::result::Error::DatabaseError(
+                DatabaseErrorKind::UniqueViolation,
+                _,
+            ))) => {
+                // Unique key violation: this is probably a retry.  Because the shard count is part of the unique key,
+                // if we see a unique key violation it means that the creation request's shard count matches the previous
+                // creation's shard count.
+                tracing::info!("Tenant shards already present in database, proceeding with idempotent creation...");
+            }
+            // Any other database error is unexpected and a bug.
+            Err(e) => return Err(ApiError::InternalServerError(anyhow::anyhow!(e))),
+        };
 
         let (waiters, response_shards) = {
             let mut locked = self.inner.write().unwrap();
diff --git a/test_runner/fixtures/neon_fixtures.py b/test_runner/fixtures/neon_fixtures.py
index f22ce10c20..3d60f9bef5 100644
--- a/test_runner/fixtures/neon_fixtures.py
+++ b/test_runner/fixtures/neon_fixtures.py
@@ -2126,6 +2126,8 @@ class NeonStorageController(MetricsGetter):
             shard_params = {"count": shard_count}
             if shard_stripe_size is not None:
                 shard_params["stripe_size"] = shard_stripe_size
+            else:
+                shard_params["stripe_size"] = 32768
 
             body["shard_parameters"] = shard_params
 
@@ -2139,6 +2141,7 @@ class NeonStorageController(MetricsGetter):
             json=body,
             headers=self.headers(TokenScope.PAGE_SERVER_API),
         )
+        response.raise_for_status()
         log.info(f"tenant_create success: {response.json()}")
 
     def locate(self, tenant_id: TenantId) -> list[dict[str, Any]]:
diff --git a/test_runner/regress/test_sharding_service.py b/test_runner/regress/test_sharding_service.py
index b7488cadd6..fc6c137667 100644
--- a/test_runner/regress/test_sharding_service.py
+++ b/test_runner/regress/test_sharding_service.py
@@ -89,6 +89,11 @@ def test_sharding_service_smoke(
     for tid in tenant_ids:
         env.neon_cli.create_tenant(tid, shard_count=shards_per_tenant)
 
+    # Repeating a creation should be idempotent (we are just testing it doesn't return an error)
+    env.storage_controller.tenant_create(
+        tenant_id=next(iter(tenant_ids)), shard_count=shards_per_tenant
+    )
+
     for node_id, count in get_node_shard_counts(env, tenant_ids).items():
         # we used a multiple of pagservers for the total shard count,
         # so expect equal number on all pageservers