diff --git a/tests/uchar_test.cpp b/tests/uchar_test.cpp
index 1936a8d..e321d83 100644
--- a/tests/uchar_test.cpp
+++ b/tests/uchar_test.cpp
@@ -304,46 +304,86 @@
 TEST(uchar, mbrtoc32) {
   char32_t out[8];
 
+  // C23 says:
+  //
+  // Returns:
+  //
+  //     0 if the next n or fewer bytes complete the multibyte character that
+  //     corresponds to the null wide character (which is the value stored).
+  //
+  //     (size_t)(-2) if the next n bytes contribute to an incomplete (but
+  //     potentially valid) multibyte character, and all n bytes have been
+  //     processed (no value is stored).
+  //
+  // Bionic historically interpreted the behavior when n is 0 to be the next 0
+  // bytes decoding to the null. That's a pretty bad interpretation, and both
+  // glibc and musl return -2 for that case.
+  //
+  // The test currently checks the incorrect behavior for bionic because gtest
+  // doesn't support explicit xfail annotations. The behavior difference here
+  // should be fixed, but danalbert wants to add more tests before tackling the
+  // bugs.
+#ifdef __ANDROID__
+  const size_t expected_result_for_zero_length = 0U;
+#else
+  const size_t expected_result_for_zero_length = static_cast<size_t>(-2);
+#endif
+
   out[0] = L'x';
-  ASSERT_EQ(0U, mbrtoc32(out, "hello", 0, nullptr));
-  ASSERT_EQ(static_cast<char32_t>(L'x'), out[0]);
+  EXPECT_EQ(expected_result_for_zero_length, mbrtoc32(out, "hello", 0, nullptr));
+  EXPECT_EQ(static_cast<char32_t>(L'x'), out[0]);
 
-  ASSERT_EQ(0U, mbrtoc32(out, "hello", 0, nullptr));
-  ASSERT_EQ(0U, mbrtoc32(out, "", 0, nullptr));
-  ASSERT_EQ(1U, mbrtoc32(out, "hello", 1, nullptr));
-  ASSERT_EQ(static_cast<char32_t>(L'h'), out[0]);
+  EXPECT_EQ(expected_result_for_zero_length, mbrtoc32(out, "hello", 0, nullptr));
+  EXPECT_EQ(expected_result_for_zero_length, mbrtoc32(out, "", 0, nullptr));
+  EXPECT_EQ(1U, mbrtoc32(out, "hello", 1, nullptr));
+  EXPECT_EQ(static_cast<char32_t>(L'h'), out[0]);
 
-  ASSERT_EQ(0U, mbrtoc32(nullptr, "hello", 0, nullptr));
-  ASSERT_EQ(0U, mbrtoc32(nullptr, "", 0, nullptr));
-  ASSERT_EQ(1U, mbrtoc32(nullptr, "hello", 1, nullptr));
+  EXPECT_EQ(expected_result_for_zero_length, mbrtoc32(nullptr, "hello", 0, nullptr));
+  EXPECT_EQ(expected_result_for_zero_length, mbrtoc32(nullptr, "", 0, nullptr));
+  EXPECT_EQ(1U, mbrtoc32(nullptr, "hello", 1, nullptr));
 
-  ASSERT_EQ(0U, mbrtoc32(nullptr, nullptr, 0, nullptr));
+  EXPECT_EQ(0U, mbrtoc32(nullptr, nullptr, 0, nullptr));
 
   ASSERT_STREQ("C.UTF-8", setlocale(LC_CTYPE, "C.UTF-8"));
   uselocale(LC_GLOBAL_LOCALE);
 
   // 1-byte UTF-8.
-  ASSERT_EQ(1U, mbrtoc32(out, "abcdef", 6, nullptr));
-  ASSERT_EQ(static_cast<char32_t>(L'a'), out[0]);
+  EXPECT_EQ(1U, mbrtoc32(out, "abcdef", 6, nullptr));
+  EXPECT_EQ(static_cast<char32_t>(L'a'), out[0]);
   // 2-byte UTF-8.
-  ASSERT_EQ(2U, mbrtoc32(out, "\xc2\xa2" "cdef", 6, nullptr));
-  ASSERT_EQ(static_cast<char32_t>(0x00a2), out[0]);
+  EXPECT_EQ(2U, mbrtoc32(out,
+                         "\xc2\xa2"
+                         "cdef",
+                         6, nullptr));
+  EXPECT_EQ(static_cast<char32_t>(0x00a2), out[0]);
   // 3-byte UTF-8.
-  ASSERT_EQ(3U, mbrtoc32(out, "\xe2\x82\xac" "def", 6, nullptr));
-  ASSERT_EQ(static_cast<char32_t>(0x20ac), out[0]);
+  EXPECT_EQ(3U, mbrtoc32(out,
+                         "\xe2\x82\xac"
+                         "def",
+                         6, nullptr));
+  EXPECT_EQ(static_cast<char32_t>(0x20ac), out[0]);
   // 4-byte UTF-8.
-  ASSERT_EQ(4U, mbrtoc32(out, "\xf0\xa4\xad\xa2" "ef", 6, nullptr));
-  ASSERT_EQ(static_cast<char32_t>(0x24b62), out[0]);
+  EXPECT_EQ(4U, mbrtoc32(out,
+                         "\xf0\xa4\xad\xa2"
+                         "ef",
+                         6, nullptr));
+  EXPECT_EQ(static_cast<char32_t>(0x24b62), out[0]);
 #if defined(__BIONIC__) // glibc allows this.
   // Illegal 5-byte UTF-8.
   errno = 0;
-  ASSERT_EQ(static_cast<size_t>(-1), mbrtoc32(out, "\xf8\xa1\xa2\xa3\xa4" "f", 6, nullptr));
-  ASSERT_EQ(EILSEQ, errno);
+  EXPECT_EQ(static_cast<size_t>(-1), mbrtoc32(out,
+                                              "\xf8\xa1\xa2\xa3\xa4"
+                                              "f",
+                                              6, nullptr));
+  EXPECT_EQ(EILSEQ, errno);
 #endif
   // Illegal over-long sequence.
   errno = 0;
-  ASSERT_EQ(static_cast<size_t>(-1), mbrtoc32(out, "\xf0\x82\x82\xac" "ef", 6, nullptr));
-  ASSERT_EQ(EILSEQ, errno);
+  EXPECT_EQ(static_cast<size_t>(-1), mbrtoc32(out,
+                                              "\xf0\x82\x82\xac"
+                                              "ef",
+                                              6, nullptr));
+  EXPECT_EQ(EILSEQ, errno);
 }
 
 void test_mbrtoc32_incomplete(mbstate_t* ps) {