diff --git a/ulid/__init__.py b/ulid/__init__.py
index 1ff7164..0eaeb33 100644
--- a/ulid/__init__.py
+++ b/ulid/__init__.py
@@ -70,7 +70,9 @@ class ULID:
     def __init__(self, value: bytes | None = None) -> None:
         if value is not None and len(value) != constants.BYTES_LEN:
             raise ValueError("ULID has to be exactly 16 bytes long.")
-        self.bytes: bytes = value or ULID.from_timestamp(time.time()).bytes
+        self.bytes: bytes = (
+            value or ULID.from_timestamp(time.time_ns() // constants.NANOSECS_IN_MILLISECS).bytes
+        )
 
     @classmethod
     @validate_type(datetime)
diff --git a/ulid/constants.py b/ulid/constants.py
index a0a1995..bc182c6 100644
--- a/ulid/constants.py
+++ b/ulid/constants.py
@@ -1,4 +1,5 @@
 MILLISECS_IN_SECS = 1000
+NANOSECS_IN_MILLISECS = 1000000
 
 TIMESTAMP_LEN = 6
 RANDOMNESS_LEN = 10