diff --git a/hera_cal/io.py b/hera_cal/io.py
index 9c7cd1596..3adf9fcd3 100644
--- a/hera_cal/io.py
+++ b/hera_cal/io.py
@@ -2204,9 +2204,13 @@ def write_vis(fname, data, lst_array, freq_array, antpos, time_array=None, flags
     # configure baselines
     antpairs = np.repeat(np.array(antpairs), Ntimes, axis=0)
 
+    antpairs_int = antpairs.astype(np.uint64)
+    if not np.allclose(antpairs, antpairs_int):
+        raise ValueError("antenna numbers must be non-negative integers")
+
     # get ant_1_array, ant_2_array
-    ant_1_array = antpairs[:, 0]
-    ant_2_array = antpairs[:, 1]
+    ant_1_array = antpairs_int[:, 0]
+    ant_2_array = antpairs_int[:, 1]
 
     # get baseline array
     baseline_array = 2048 * (ant_1_array + 1) + (ant_2_array + 1) + 2**16