diff --git a/src/Storages/MergeTree/MergeTreePartition.cpp b/src/Storages/MergeTree/MergeTreePartition.cpp
index 50848584207..471905c581d 100644
--- a/src/Storages/MergeTree/MergeTreePartition.cpp
+++ b/src/Storages/MergeTree/MergeTreePartition.cpp
@@ -228,6 +228,9 @@ Block MergeTreePartition::executePartitionByExpression(const StorageMetadataPtr
 KeyDescription MergeTreePartition::adjustPartitionKey(const StorageMetadataPtr & metadata_snapshot, ContextPtr context)
 {
     const auto & partition_key = metadata_snapshot->getPartitionKey();
+    if (!partition_key.definition_ast)
+        return partition_key;
+
     ASTPtr ast_copy = partition_key.definition_ast->clone();
 
     /// Implementation of modulo function was changed from 8bit result type to 16bit. For backward compatibility partition by expression is always