diff --git a/sdks/python/pmxt/_hosted_mappers.py b/sdks/python/pmxt/_hosted_mappers.py
index 30f0adab..dfa13cfd 100644
--- a/sdks/python/pmxt/_hosted_mappers.py
+++ b/sdks/python/pmxt/_hosted_mappers.py
@@ -15,7 +15,7 @@
 from .errors import InvalidOrder
 from .models import Balance, BuiltOrder, Order, Position, UserTrade
 
-SIX_DEC_SCALE = 1_000_000
+_SIX_DEC_SCALE = 1_000_000
 
 _T = TypeVar("_T")
 
@@ -23,7 +23,7 @@
 def to_6dec(amount: float | str | Decimal) -> int:
     """Convert a decimal amount to integer micro-units with no rounding."""
     d = Decimal(str(amount))
-    scaled = d * SIX_DEC_SCALE
+    scaled = d * _SIX_DEC_SCALE
     if scaled != scaled.to_integral_value():
         raise InvalidOrder(f"amount precision exceeds 6 decimals: {amount!r}")
     return int(scaled)
diff --git a/sdks/python/tests/test_hosted_mappers.py b/sdks/python/tests/test_hosted_mappers.py
index 95082577..af9f65dc 100644
--- a/sdks/python/tests/test_hosted_mappers.py
+++ b/sdks/python/tests/test_hosted_mappers.py
@@ -29,6 +29,11 @@ def _mapper(*names):
 to_6dec = _hosted_mappers.to_6dec
 
 
+def test_six_decimal_scale_is_module_private():
+    assert not hasattr(_hosted_mappers, "SIX_DEC_SCALE")
+    assert _hosted_mappers._SIX_DEC_SCALE == 1_000_000
+
+
 def _iso_ms(value: str) -> int:
     return int(datetime.fromisoformat(value.replace("Z", "+00:00")).timestamp() * 1000)