diff --git a/iox_catalog/src/mem.rs b/iox_catalog/src/mem.rs
index e69be745a6..8beb2d3418 100644
--- a/iox_catalog/src/mem.rs
+++ b/iox_catalog/src/mem.rs
@@ -8,14 +8,14 @@ use crate::{
         Result, ShardRepo, SoftDeletedRows, TableRepo, TopicMetadataRepo, Transaction,
     },
     metrics::MetricDecorator,
-    DEFAULT_MAX_COLUMNS_PER_TABLE, DEFAULT_MAX_TABLES,
+    DEFAULT_MAX_COLUMNS_PER_TABLE, DEFAULT_MAX_TABLES, SHARED_TOPIC_ID, SHARED_TOPIC_NAME,
 };
 use async_trait::async_trait;
 use data_types::{
     Column, ColumnId, ColumnType, CompactionLevel, Namespace, NamespaceId, ParquetFile,
     ParquetFileId, ParquetFileParams, Partition, PartitionId, PartitionKey, QueryPool, QueryPoolId,
     SequenceNumber, Shard, ShardId, ShardIndex, SkippedCompaction, Table, TableId, Timestamp,
-    TopicId, TopicMetadata,
+    TopicId, TopicMetadata, TRANSITION_SHARD_ID, TRANSITION_SHARD_INDEX,
 };
 use iox_time::{SystemProvider, TimeProvider};
 use observability_deps::tracing::warn;
@@ -123,7 +123,35 @@ impl Display for MemCatalog {
 #[async_trait]
 impl Catalog for MemCatalog {
     async fn setup(&self) -> Result<(), Error> {
-        // nothing to do
+        let guard = Arc::clone(&self.collections).lock_owned().await;
+        let stage = guard.clone();
+        let mut transaction = MemTxn {
+            inner: MemTxnInner::Txn {
+                guard,
+                stage,
+                finalized: false,
+            },
+            time_provider: self.time_provider(),
+        };
+        let stage = transaction.stage();
+
+        // We need to manually insert the topic here so that we can create the transition shard
+        // below.
+        let topic = TopicMetadata {
+            id: SHARED_TOPIC_ID,
+            name: SHARED_TOPIC_NAME.to_string(),
+        };
+        stage.topics.push(topic.clone());
+
+        // The transition shard must exist and must have magic ID and INDEX.
+        let shard = Shard {
+            id: TRANSITION_SHARD_ID,
+            topic_id: topic.id,
+            shard_index: TRANSITION_SHARD_INDEX,
+            min_unpersisted_sequence_number: SequenceNumber::new(0),
+        };
+        stage.shards.push(shard);
+        transaction.commit_inplace().await?;
         Ok(())
     }