diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4e4dfce5..a9e5f3ed 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,10 @@
 # Changelog
 ## [Unreleased]
 
+### Fixed
+
+- zstd compression uses a fresh `zstandard` compressor/decompressor per call instead of shared module-level singletons, fixing process segfaults when ingester workers compress documents concurrently (Python < 3.14).
+
 ## [0.61.0] - 2026-06-23
 
 ### Added
diff --git a/haiku_rag_slim/haiku/rag/store/compression.py b/haiku_rag_slim/haiku/rag/store/compression.py
index 5aecf464..2202cba8 100644
--- a/haiku_rag_slim/haiku/rag/store/compression.py
+++ b/haiku_rag_slim/haiku/rag/store/compression.py
@@ -10,15 +10,18 @@ try:  # pragma: no cover
 except ImportError:
     from zstandard import ZstdCompressor, ZstdDecompressor, get_frame_parameters
 
-    _zstd_compressor = ZstdCompressor()
-    _zstd_decompressor = ZstdDecompressor()
-
+    # ZstdCompressor/ZstdDecompressor are not thread-safe: each wraps a single
+    # reused ZSTD_CCtx/ZSTD_DCtx, and concurrent .compress()/.decompress() calls
+    # corrupt that context and segfault in the C backend. Ingestion drives this
+    # path from multiple worker threads (asyncio.to_thread in
+    # _prepare_document_from_docling), so construct a fresh instance per call
+    # rather than sharing a module-level singleton.
     def _zstd_compress(data: bytes) -> bytes:
-        return _zstd_compressor.compress(data)
+        return ZstdCompressor().compress(data)
 
     def _zstd_decompress(data: bytes) -> bytes:
         content_size = get_frame_parameters(data).content_size
-        return _zstd_decompressor.decompress(data, max_output_size=content_size)
+        return ZstdDecompressor().decompress(data, max_output_size=content_size)
 
 
 def compress_json(json_str: str) -> bytes:
diff --git a/tests/store/test_compression.py b/tests/store/test_compression.py
index 9532b312..45d3f4b2 100644
--- a/tests/store/test_compression.py
+++ b/tests/store/test_compression.py
@@ -1,4 +1,5 @@
 import json
+from concurrent.futures import ThreadPoolExecutor
 
 from haiku.rag.store.compression import (
     compress_docling_split,
@@ -24,6 +25,27 @@ class TestJsonCompression:
         compressed = compress_json('{"test": true}')
         assert compressed[:4] == b"\x28\xb5\x2f\xfd"
 
+    def test_concurrent_compress_decompress_is_safe(self):
+        """Compression must be safe under concurrent threads.
+
+        Ingestion offloads compression to worker threads via
+        asyncio.to_thread; sharing a single zstandard compressor/decompressor
+        across threads corrupts its internal C context and segfaults the
+        process. Hammer both paths from many threads to guard against a
+        regression to module-level singletons.
+        """
+        payloads = [
+            json.dumps({"i": i, "text": f"document body {i} " * 200}) for i in range(64)
+        ]
+
+        def roundtrip(json_str: str) -> str:
+            return decompress_json(compress_json(json_str))
+
+        with ThreadPoolExecutor(max_workers=16) as pool:
+            results = list(pool.map(roundtrip, payloads * 8))
+
+        assert results == (payloads * 8)
+
 
 class TestDoclingCompressionSplit:
     def test_split_with_pages(self):