diff --git a/api/core/rag/index_processor/index_processor.py b/api/core/rag/index_processor/index_processor.py
index a6d1db214b0..825ae012269 100644
--- a/api/core/rag/index_processor/index_processor.py
+++ b/api/core/rag/index_processor/index_processor.py
@@ -35,7 +35,10 @@ class IndexProcessor:
         if "parent_mode" in preview:
             data.parent_mode = preview["parent_mode"]
 
-        for item in preview["preview"]:
+        # Different index processors return different preview shapes:
+        # - paragraph/parent-child processors: {"preview": [...]}
+        # - QA processor: {"qa_preview": [...]} (no "preview" key)
+        for item in preview.get("preview", []):
             if "content" in item and "child_chunks" in item:
                 data.preview.append(
                     PreviewItem(content=item["content"], child_chunks=item["child_chunks"], summary=None)
@@ -44,6 +47,10 @@ class IndexProcessor:
                 data.qa_preview.append(QaPreview(question=item["question"], answer=item["answer"]))
             elif "content" in item:
                 data.preview.append(PreviewItem(content=item["content"], child_chunks=None, summary=None))
+
+        for item in preview.get("qa_preview", []):
+            if "question" in item and "answer" in item:
+                data.qa_preview.append(QaPreview(question=item["question"], answer=item["answer"]))
         return data
 
     def index_and_clean(
diff --git a/api/tests/unit_tests/core/rag/indexing/test_index_processor.py b/api/tests/unit_tests/core/rag/indexing/test_index_processor.py
new file mode 100644
index 00000000000..a3f284955bc
--- /dev/null
+++ b/api/tests/unit_tests/core/rag/indexing/test_index_processor.py
@@ -0,0 +1,15 @@
+from core.rag.index_processor.index_processor import IndexProcessor
+
+
+class TestIndexProcessor:
+    def test_format_preview_supports_qa_preview_shape(self) -> None:
+        preview = IndexProcessor().format_preview(
+            "qa_model",
+            {"qa_chunks": [{"question": "Q1", "answer": "A1"}]},
+        )
+
+        assert preview.chunk_structure == "qa_model"
+        assert preview.total_segments == 1
+        assert len(preview.qa_preview) == 1
+        assert preview.qa_preview[0].question == "Q1"
+        assert preview.qa_preview[0].answer == "A1"