diff --git a/datastore/api/responses.py b/datastore/api/responses.py
index 543e2df..19f9aa1 100644
--- a/datastore/api/responses.py
+++ b/datastore/api/responses.py
@@ -27,11 +27,12 @@ def _orjson_default(obj: Any) -> Any:
     if hasattr(obj, "model_dump"):
         return obj.model_dump(exclude_none=True)
     # BigQuery `NUMERIC` / `BIGNUMERIC` columns come back as Decimal —
-    # JSON has no native form, and orjson refuses by default. Stringify
-    # to preserve full precision (NUMERIC = 38 digits, BIGNUMERIC = 76+,
-    # both beyond IEEE-754 double).
+    # JSON has no native form, and orjson refuses by default. Emit as a
+    # JSON number so clients can do arithmetic without parsing a string;
+    # values past ~15 significant digits round to the nearest IEEE-754
+    # double (full-precision callers should CAST to STRING in SQL).
     if isinstance(obj, Decimal):
-        return str(obj)
+        return float(obj)
     # `BYTES` columns come back as raw `bytes`; base64-encode so the
     # response stays UTF-8 and round-trippable.
     if isinstance(obj, bytes):
diff --git a/datastore/services/streaming.py b/datastore/services/streaming.py
index 12df494..883cd1e 100644
--- a/datastore/services/streaming.py
+++ b/datastore/services/streaming.py
@@ -43,17 +43,17 @@ def _json_default(obj: Any) -> Any:
     """Serialise types `orjson` refuses out of the box.
 
     BigQuery `NUMERIC` / `BIGNUMERIC` columns come back as
-    `decimal.Decimal`, which has no native JSON representation.
-    Stringifying preserves full precision (NUMERIC is 38 digits,
-    BIGNUMERIC is 76+ — beyond what a JSON number / IEEE-754 double
-    can represent without loss) and matches CKAN's datastore
-    convention of returning high-precision numerics as strings.
+    `decimal.Decimal`. Emit them as JSON numbers so clients can do
+    arithmetic without parsing a string. The cost is that values past
+    ~15 significant digits round to the nearest IEEE-754 double —
+    full-precision callers should `CAST(... AS STRING)` in
+    `datastore_search_sql` instead.
 
     `bytes` (BigQuery `BYTES` columns) are base64-encoded so the
     response stays UTF-8 and round-trippable.
     """
     if isinstance(obj, Decimal):
-        return str(obj)
+        return float(obj)
     if isinstance(obj, bytes):
         return base64.b64encode(obj).decode("ascii")
     raise TypeError(
diff --git a/tests/test_streaming.py b/tests/test_streaming.py
index 4377f8b..4a0cc49 100644
--- a/tests/test_streaming.py
+++ b/tests/test_streaming.py
@@ -28,8 +28,7 @@ def _join(parts: list[bytes]) -> str:
 
 def test_records_object_array_serialises_decimal_and_bytes() -> None:
     """Rows with NUMERIC (Decimal) + BYTES values must stream without
-    blowing up; Decimal is stringified (preserves precision); bytes is
-    base64-encoded."""
+    blowing up; Decimal lands as a JSON number; bytes is base64-encoded."""
     rows = iter(
         [
             ("DCL", Decimal("47.82"), b"\x00\xff"),
@@ -44,15 +43,19 @@ def test_records_object_array_serialises_decimal_and_bytes() -> None:
     assert records == [
         {
             "product_code": "DCL",
-            "clearing_price_gbp_per_mwh": "47.82",
+            "clearing_price_gbp_per_mwh": 47.82,
             "signature": "AP8=",                 # b64("\x00\xff")
         },
         {
             "product_code": "DCH",
-            "clearing_price_gbp_per_mwh": "1E-38",
+            "clearing_price_gbp_per_mwh": 1e-38,
             "signature": "YWJj",                 # b64(b"abc")
         },
     ]
+    # Confirm the type, not just the value — `47.82 == "47.82"` would be
+    # False but the eq above could pass with both as strings if the field
+    # ever flipped back. Pin the JSON number contract explicitly.
+    assert isinstance(records[0]["clearing_price_gbp_per_mwh"], float)
 
 
 def test_records_array_array_serialises_decimal_and_bytes() -> None:
@@ -62,7 +65,8 @@ def test_records_array_array_serialises_decimal_and_bytes() -> None:
     body = _join(list(_records_array_array(rows)))
     records = json.loads(body)
 
-    assert records == [["DCL", "47.82", "AP8="]]
+    assert records == [["DCL", 47.82, "AP8="]]
+    assert isinstance(records[0][1], float)
 
 
 def test_unsupported_type_still_raises() -> None: