diff --git a/artiq/language/core.py b/artiq/language/core.py
index 02f89899b..0c695be21 100644
--- a/artiq/language/core.py
+++ b/artiq/language/core.py
@@ -347,7 +347,7 @@ def time_to_cycles(time, core=None):
     """
     if core is None:
         raise ValueError("Core device must be specified for time conversion")
-    return int64(time.amount//core.runtime_env.ref_period)
+    return round64(time.amount//core.runtime_env.ref_period)
 
 
 def cycles_to_time(cycles, core=None):
diff --git a/artiq/transforms/lower_time.py b/artiq/transforms/lower_time.py
index 2b0c136fa..be84a57f8 100644
--- a/artiq/transforms/lower_time.py
+++ b/artiq/transforms/lower_time.py
@@ -11,7 +11,7 @@ def _time_to_cycles(ref_period, node):
                   right=value_to_ast(ref_period)),
         node)
     return ast.copy_location(
-        ast.Call(func=ast.Name("int64", ast.Load()),
+        ast.Call(func=ast.Name("round64", ast.Load()),
                  args=[divided],
                  keywords=[], starargs=[], kwargs=[]),
         divided)