diff --git a/tests/Android.bp b/tests/Android.bp
index 476b8f5..0f9af41 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -406,6 +406,7 @@
         "string_nofortify_test.cpp",
         "string_test.cpp",
         "string_posix_strerror_r_test.cpp",
+        "string_posix_strerror_r_wrapper.cpp",
         "strings_nofortify_test.cpp",
         "strings_test.cpp",
         "struct_layout_test.cpp",
diff --git a/tests/string_posix_strerror_r_test.cpp b/tests/string_posix_strerror_r_test.cpp
index 67b3c1f..c4757ae 100644
--- a/tests/string_posix_strerror_r_test.cpp
+++ b/tests/string_posix_strerror_r_test.cpp
@@ -14,51 +14,40 @@
  * limitations under the License.
  */
 
-#undef _GNU_SOURCE
-#include <features.h> // Get __BIONIC__ or __GLIBC__ so we can tell what we're using.
-
-#if defined(__GLIBC__)
-
-// At the time of writing, libcxx -- which is dragged in by gtest -- assumes
-// declarations from glibc of things that aren't available without _GNU_SOURCE.
-// This means we can't even build this test (which is a problem because that
-// means it doesn't get included in CTS).
-// For glibc 2.15, the symbols in question are:
-//   at_quick_exit, quick_exit, vasprintf, strtoll_l, strtoull_l, and strtold_l.
-
-# if __GLIBC_PREREQ(2, 19)
-#  error check whether we can build this now...
-# endif
-
-#else
-
-#include <string.h>
-
 #include <errno.h>
 #include <gtest/gtest.h>
 
+// Defined in string_posix_strerror_r_wrapper.cpp as a wrapper around the posix
+// strerror_r to work around an incompatibility between libc++ (required by
+// gtest) and !_GNU_SOURCE.
+int posix_strerror_r(int errnum, char* buf, size_t buflen);
+
 TEST(string, posix_strerror_r) {
   char buf[256];
 
   // Valid.
-  ASSERT_EQ(0, strerror_r(0, buf, sizeof(buf)));
+  ASSERT_EQ(0, posix_strerror_r(0, buf, sizeof(buf)));
   ASSERT_STREQ("Success", buf);
-  ASSERT_EQ(0, strerror_r(1, buf, sizeof(buf)));
+  ASSERT_EQ(0, posix_strerror_r(1, buf, sizeof(buf)));
   ASSERT_STREQ("Operation not permitted", buf);
 
+#if defined(__BIONIC__)
   // Invalid.
-  ASSERT_EQ(0, strerror_r(-1, buf, sizeof(buf)));
+  ASSERT_EQ(0, posix_strerror_r(-1, buf, sizeof(buf)));
   ASSERT_STREQ("Unknown error -1", buf);
-  ASSERT_EQ(0, strerror_r(1234, buf, sizeof(buf)));
+  ASSERT_EQ(0, posix_strerror_r(1234, buf, sizeof(buf)));
   ASSERT_STREQ("Unknown error 1234", buf);
+#else
+  // glibc returns EINVAL for unknown errors
+  ASSERT_EQ(EINVAL, posix_strerror_r(-1, buf, sizeof(buf)));
+  ASSERT_EQ(EINVAL, posix_strerror_r(1234, buf, sizeof(buf)));
+#endif
 
   // Buffer too small.
   errno = 0;
   memset(buf, 0, sizeof(buf));
-  ASSERT_EQ(ERANGE, strerror_r(EPERM, buf, 2));
+  ASSERT_EQ(ERANGE, posix_strerror_r(EPERM, buf, 2));
   ASSERT_STREQ("O", buf);
   // POSIX strerror_r returns an error without updating errno.
   ASSERT_EQ(0, errno);
 }
-
-#endif
diff --git a/tests/string_posix_strerror_r_wrapper.cpp b/tests/string_posix_strerror_r_wrapper.cpp
new file mode 100644
index 0000000..78d5d90
--- /dev/null
+++ b/tests/string_posix_strerror_r_wrapper.cpp
@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#undef _GNU_SOURCE
+#include <string.h>
+
+// At the time of writing, libcxx -- which is dragged in by gtest -- assumes
+// declarations from glibc of things that aren't available without _GNU_SOURCE.
+// This means we can't even build a test that directly calls the posix
+// strerror_r.  Add a wrapper in a separate file that doesn't use any gtest.
+// For glibc 2.15, the symbols in question are:
+//   at_quick_exit, quick_exit, vasprintf, strtoll_l, strtoull_l, and strtold_l.
+
+int posix_strerror_r(int errnum, char* buf, size_t buflen) {
+  return strerror_r(errnum, buf, buflen);
+}