@@ -47,7 +47,7 @@
     dimensionless_unscaled,
 )
 from astropy.utils import isiterable
-from astropy.utils.compat import NUMPY_LT_1_23, NUMPY_LT_2_0
+from astropy.utils.compat import NUMPY_LT_1_23, NUMPY_LT_1_24, NUMPY_LT_2_0
 
 if NUMPY_LT_2_0:
     import numpy.core as np_core
@@ -918,16 +918,26 @@ def unique(
     return_counts=False,
     axis=None,
     *,
-    equal_nan=True,  # new in numpy 1.24
+    equal_nan=None,  # new in numpy 1.24
 ):
     unit = ar.unit
     n_index = sum(bool(i) for i in (return_index, return_inverse, return_counts))
     if n_index:
         unit = [unit] + n_index * [None]
 
+    if NUMPY_LT_1_24:
+        if equal_nan is not None:
+            raise TypeError("unique() got an unexpected keyword argument 'equal_nan'")
+        else:
+            kwargs = {}
+    else:
+        if equal_nan is None:
+            equal_nan = False
+        kwargs = {"equal_nan": equal_nan}
+
     return (
         (ar.value, return_index, return_inverse, return_counts, axis),
-        {"equal_nan": equal_nan},
+        kwargs,
         unit,
         None,
     )