diff --git a/src/api/schemas.py b/src/api/schemas.py
index 7dd77ea..d987200 100644
--- a/src/api/schemas.py
+++ b/src/api/schemas.py
@@ -247,7 +247,7 @@ class HistoryEntry(BaseModel):
     }
 
 
-SourceSystemValue = Literal["GITHUB", "JIRA", "CONFLUENCE", "UPLOAD"]
+SourceSystemValue = Literal["GITHUB", "BITBUCKET", "JIRA", "CONFLUENCE", "UPLOAD"]
 
 
 class ProjectScopedRequest(BaseModel):
diff --git a/src/rag/types.py b/src/rag/types.py
index ecd2eac..b6e6488 100644
--- a/src/rag/types.py
+++ b/src/rag/types.py
@@ -4,7 +4,7 @@
 from ingestion.source_role import SourceRole
 
 ChunkKind = Literal["text", "code", "pdf", "image"]
-SourceSystem = Literal["GITHUB", "JIRA", "CONFLUENCE", "UPLOAD"]
+SourceSystem = Literal["GITHUB", "BITBUCKET", "JIRA", "CONFLUENCE", "UPLOAD"]
 
 
 def is_chunk_kind(value: str) -> TypeGuard[ChunkKind]:
@@ -12,7 +12,7 @@ def is_chunk_kind(value: str) -> TypeGuard[ChunkKind]:
 
 
 def is_source_system(value: str) -> TypeGuard[SourceSystem]:
-    return value in ("GITHUB", "JIRA", "CONFLUENCE", "UPLOAD")
+    return value in ("GITHUB", "BITBUCKET", "JIRA", "CONFLUENCE", "UPLOAD")
 
 
 @dataclass(frozen=True)
diff --git a/tests/api/test_chat.py b/tests/api/test_chat.py
index cc029f5..193a007 100644
--- a/tests/api/test_chat.py
+++ b/tests/api/test_chat.py
@@ -152,6 +152,66 @@ def stream(self, messages: list[Message]) -> Iterator[LLMStreamEvent]:
     ]
 
 
+@pytest.mark.parametrize("value", ["BITBUCKET", "bitbucket"])
+def test_chat_accepts_a_bitbucket_source_filter(
+    client: tuple[TestClient, StubLLMClient, StubVectorStore], value: str
+) -> None:
+    http_client, _, store = client
+    embedding = [1.0] + [0.0] * 767
+
+    class AnsweringLLM(StubLLMClient):
+        def stream(self, messages: list[Message]) -> Iterator[LLMStreamEvent]:
+            yield TextDelta("From Bitbucket.")
+
+    app.dependency_overrides[get_llm] = lambda: AnsweringLLM(embedding=embedding)
+    store.add(
+        [
+            Chunk(
+                id="chunk-1",
+                artifact_id="doc-1",
+                filename="widgets.md",
+                text="The widgets service retries three times.",
+                embedding=embedding,
+                project_ids=(_PROJECT,),
+                source_system="BITBUCKET",
+            )
+        ]
+    )
+
+    response = http_client.post(
+        "/api/v1/chat",
+        json={
+            "prompt": "How does widgets retry?",
+            "projectId": _PROJECT,
+            "filters": {"source_systems": [value]},
+        },
+    )
+
+    # Before BITBUCKET was a known source system this was rejected with a 422.
+    assert response.status_code == 200
+    events = parse_sse_events(response.text)
+    assert [event["content"] for event in events if event["type"] == "token"] == [
+        "From Bitbucket."
+    ]
+
+
+def test_chat_still_rejects_an_unknown_source_filter(
+    client: tuple[TestClient, StubLLMClient, StubVectorStore],
+) -> None:
+    http_client, _, _ = client
+
+    response = http_client.post(
+        "/api/v1/chat",
+        json={
+            "prompt": "Anything?",
+            "projectId": _PROJECT,
+            "filters": {"source_systems": ["GITLAB"]},
+        },
+    )
+
+    assert response.status_code == 422
+
+
 def test_chat_emits_citation_when_chunks_exist(
     client: tuple[TestClient, StubLLMClient, StubVectorStore],
 ) -> None:
diff --git a/tests/rag/test_filters.py b/tests/rag/test_filters.py
index b345e11..8b5639b 100644
--- a/tests/rag/test_filters.py
+++ b/tests/rag/test_filters.py
@@ -4,9 +4,10 @@
     decode_project_ids,
     encode_project_ids,
     matches_retrieval_filters,
+    normalize_source_system,
     where_filter_for_chroma,
 )
-from rag.types import Chunk, RetrievalFilters
+from rag.types import Chunk, RetrievalFilters, is_source_system
 
 
 def test_source_system_filter_matches_allowed_system() -> None:
@@ -54,6 +55,39 @@ def test_confluence_source_system_survives_ingest_and_filtering() -> None:
     )
 
 
+def test_bitbucket_source_system_survives_ingest_and_filtering() -> None:
+    # Without BITBUCKET in the known systems the ingest silently tagged the chunk
+    # with no source system, so a Bitbucket filter could never find it.
+    chunk = to_chunk(
+        ParsedChunk(
+            content="Why the widgets service retries",
+            kind="text",
+            metadata={"filename": "widgets.md"},
+        ),
+        artifact_id="bitbucket:acme/widgets:FILE:widgets.md",
+        embedding=[1.0, 0.0],
+        artifact_type="FILE",
+        source_system="BITBUCKET",
+    )
+
+    assert chunk.source_system == "BITBUCKET"
+    assert matches_retrieval_filters(
+        chunk,
+        RetrievalFilters(source_systems=["BITBUCKET"]),
+    )
+    assert not matches_retrieval_filters(
+        chunk,
+        RetrievalFilters(source_systems=["GITHUB"]),
+    )
+
+
+def test_source_system_is_recognised_case_insensitively() -> None:
+    assert normalize_source_system("bitbucket") == "BITBUCKET"
+    assert is_source_system("BITBUCKET")
+    assert normalize_source_system("gitlab") is None
+    assert normalize_source_system(None) is None
+
+
 def test_source_timestamp_preferred_over_indexed_at() -> None:
     chunk = to_chunk(
         ParsedChunk(