diff --git a/python/copilot/generated/session_events.py b/python/copilot/generated/session_events.py
index f2e155f49..604a165c3 100644
--- a/python/copilot/generated/session_events.py
+++ b/python/copilot/generated/session_events.py
@@ -51,8 +51,8 @@ def from_timedelta(x: Any) -> timedelta:
 def to_timedelta_int(x: timedelta) -> int:
     assert isinstance(x, timedelta)
     milliseconds = x.total_seconds() * 1000.0
-    assert milliseconds.is_integer()
-    return int(milliseconds)
+    # Durations can carry sub-millisecond precision; round to the nearest whole ms.
+    return round(milliseconds)
 
 
 def to_timedelta(x: timedelta) -> float:
diff --git a/scripts/codegen/python.ts b/scripts/codegen/python.ts
index 0ba72db50..280e185cb 100644
--- a/scripts/codegen/python.ts
+++ b/scripts/codegen/python.ts
@@ -2538,8 +2538,8 @@ export function generatePythonSessionEventsCode(schema: JSONSchema7): string {
             out.push(`def to_timedelta_int(x: timedelta) -> int:`);
             out.push(`    assert isinstance(x, timedelta)`);
             out.push(`    milliseconds = x.total_seconds() * 1000.0`);
-            out.push(`    assert milliseconds.is_integer()`);
-            out.push(`    return int(milliseconds)`);
+            out.push(`    # Durations can carry sub-millisecond precision; round to the nearest whole ms.`);
+            out.push(`    return round(milliseconds)`);
             out.push(``);
             out.push(``);
         }