msgpack · methane · Jun 2, 2026 · Feb 20, 2026 · Jun 2, 2026 · methane
diff --git a/msgpack/ext.py b/msgpack/ext.py
@@ -167,4 +167,4 @@ def from_datetime(dt):

        :rtype: Timestamp
        """
-        return Timestamp(seconds=int(dt.timestamp()), nanoseconds=dt.microsecond * 1000)
+        return Timestamp(seconds=int(dt.timestamp() // 1), nanoseconds=dt.microsecond * 1000)
diff --git a/test/test_timestamp.py b/test/test_timestamp.py
@@ -103,6 +103,13 @@ def test_timestamp_datetime():

    assert Timestamp.from_datetime(ts).to_datetime() == ts

+    # Regression test: pre-epoch fractional seconds must floor toward -inf.
+    pre_epoch = datetime.datetime(1969, 12, 31, 23, 59, 59, 500000, tzinfo=utc)
+    ts_pre_epoch = Timestamp.from_datetime(pre_epoch)
+    assert ts_pre_epoch.seconds == -1
+    assert ts_pre_epoch.nanoseconds == 500000000
+    assert ts_pre_epoch.to_datetime() == pre_epoch
+

 def test_unpack_datetime():
    t = Timestamp(42, 14)
-Original file line number
+Diff line change
@@ -167,4 +167,4 @@ def from_datetime(dt):
             :rtype: Timestamp
             """
-            return Timestamp(seconds=int(dt.timestamp()), nanoseconds=dt.microsecond * 1000)
+            return Timestamp(seconds=int(dt.timestamp() // 1), nanoseconds=dt.microsecond * 1000)
         Comment thread


        

        
      

        
          


  
    
        
  



  
  
  





    
        
  
    
      
          
      

      
            methane
  

      

      

      


        Apr 21, 2026



      
    

  

  
    
      
          
    
  


        
            
  
      
              Copy link

  
              
  
      
                Copy Markdown

  
        
      
    

    
        

  
  Member


        

    
  


        
      
  
  
  
    

    There was a problem hiding this comment.


  

 
  
    

    Choose a reason for hiding this comment

    
      The reason will be displayed to describe this comment to others. Learn more.
    

    
      
      


  


  
    
      @copilot apply changes based on this feedback
    
  
  



    

        
      
  
  
    
  
  
  
    
    Sorry, something went wrong.
  

  
    
  
    
      

              Uh oh!

              
There was an error while loading. Please reload this page.


  
  


          
              
  
    
    
      
        
            
    All reactions