BUG: change `ma.mean` dtype to be consistent with `np.mean`

2 files changed, 16 insertions, 1 deletions

diff --git a/numpy/ma/core.py b/numpy/ma/core.py
index 2ff1667ba..7b099f69b 100644
--- a/numpy/ma/core.py
+++ b/numpy/ma/core.py
@@ -31,6 +31,7 @@ from functools import reduce
 import numpy as np
 import numpy.core.umath as umath
 import numpy.core.numerictypes as ntypes
+from numpy.core import multiarray as mu
 from numpy import ndarray, amax, amin, iscomplexobj, bool_, _NoValue
 from numpy import array as narray
 from numpy.lib.function_base import angle
@@ -5235,14 +5236,22 @@ class MaskedArray(ndarray):
 
         """
         kwargs = {} if keepdims is np._NoValue else {'keepdims': keepdims}
-
         if self._mask is nomask:
             result = super().mean(axis=axis, dtype=dtype, **kwargs)[()]
         else:
+            is_float16_result = False
+            if dtype is None:
+                if issubclass(self.dtype.type, (ntypes.integer, ntypes.bool_)):
+                    dtype = mu.dtype('f8')
+                elif issubclass(self.dtype.type, ntypes.float16):
+                    dtype = mu.dtype('f4')
+                    is_float16_result = True
             dsum = self.sum(axis=axis, dtype=dtype, **kwargs)
             cnt = self.count(axis=axis, **kwargs)
             if cnt.shape == () and (cnt == 0):
                 result = masked
+            elif is_float16_result:
+                result = self.dtype.type(dsum * 1. / cnt)
             else:
                 result = dsum * 1. / cnt
         if out is not None:
diff --git a/numpy/ma/tests/test_core.py b/numpy/ma/tests/test_core.py
index bf95c999a..396b90d93 100644
--- a/numpy/ma/tests/test_core.py
+++ b/numpy/ma/tests/test_core.py
@@ -4050,6 +4050,12 @@ class TestMaskedArrayMathMethods:
         assert_equal(a.max(-1), [3, 6])
         assert_equal(a.max(1), [3, 6])
 
+    def test_mean_overflow(self):
+        # Test overflow in masked arrays
+        # gh-20272
+        a = masked_array(np.full((10000, 10000), 65535, dtype=np.uint16),
+                         mask=np.zeros((10000, 10000)))
+        assert_equal(a.mean(), 65535.0)
 
 class TestMaskedArrayMathMethodsComplex:
     # Test class for miscellaneous MaskedArrays methods.