diff --git a/src/documents/search/_query.py b/src/documents/search/_query.py
index fef248253..0e8a543ab 100644
--- a/src/documents/search/_query.py
+++ b/src/documents/search/_query.py
@@ -464,8 +464,13 @@ def normalize_query(query: str) -> str:
         return " AND ".join(f"{field}:{v}" for v in values)
 
     try:
+        # Only true multi-value fields are comma-split, matching Whoosh's
+        # KEYWORD(commas=True) fields (tag, tag_id, viewer_id). A field-agnostic
+        # match would corrupt unrelated text such as URLs (http://x/a,b) or
+        # numeric values (title:10,20). tag_id is ordered before tag so the
+        # longer field name wins.
         query = regex.sub(
-            r"(\w+):([^\s\[\]]+(?:,[^\s\[\]]+)+)",
+            r"(?<!\w)(tag_id|viewer_id|tag):([^\s\[\]]+(?:,[^\s\[\]]+)+)",
             _expand,
             query,
             timeout=_REGEX_TIMEOUT,
diff --git a/src/documents/tests/search/test_query.py b/src/documents/tests/search/test_query.py
index 9c52562d3..b1efa039a 100644
--- a/src/documents/tests/search/test_query.py
+++ b/src/documents/tests/search/test_query.py
@@ -607,6 +607,28 @@ class TestNormalizeQuery:
     def test_normalize_no_commas_unchanged(self) -> None:
         assert normalize_query("bank statement") == "bank statement"
 
+    def test_normalize_expands_multi_value_id_fields(self) -> None:
+        # tag_id and viewer_id were KEYWORD(commas=True) in Whoosh too.
+        assert normalize_query("tag_id:1,2") == "tag_id:1 AND tag_id:2"
+        assert normalize_query("viewer_id:5,6") == "viewer_id:5 AND viewer_id:6"
+
+    @pytest.mark.parametrize(
+        "query",
+        [
+            pytest.param("http://example.com/a,b", id="url_with_comma"),
+            pytest.param("title:10,20", id="non_multivalue_field"),
+            pytest.param("correspondent:foo,bar", id="text_field_not_comma_split"),
+            pytest.param("content:a,b,c", id="content_field"),
+        ],
+    )
+    def test_normalize_does_not_expand_non_multi_value_fields(
+        self,
+        query: str,
+    ) -> None:
+        # Only true multi-value fields (tag/tag_id/viewer_id) comma-split, matching
+        # Whoosh's KEYWORD(commas=True) set. Everything else passes through verbatim.
+        assert normalize_query(query) == query
+
     @pytest.mark.parametrize(
         ("raw", "expected"),
         [