diff --git a/tests/string_posix_strerror_r_test.cpp b/tests/string_posix_strerror_r_test.cpp
index 09cebfe..ae3b41a 100644
--- a/tests/string_posix_strerror_r_test.cpp
+++ b/tests/string_posix_strerror_r_test.cpp
@@ -15,13 +15,23 @@
  */
 
 #undef _GNU_SOURCE
+#include <features.h> // Get __BIONIC__ or __GLIBC__ so we can tell what we're using.
 
-// Old versions of glibc (like our current host prebuilt sysroot one) have
-// headers that don't work if you #undef _GNU_SOURCE, which makes it
-// impossible to build this test.
-#include <features.h>
+#if defined(__GLIBC__)
 
-#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 __USE_GNU.
+// 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>
@@ -50,8 +60,5 @@
   // The POSIX strerror_r sets errno to ERANGE (the GNU one doesn't).
   ASSERT_EQ(ERANGE, errno);
 }
-#else
-# if __GLIBC_PREREQ(2, 15)
-#  error this test should work now
-# endif
+
 #endif
diff --git a/tests/sys_resource_test.cpp b/tests/sys_resource_test.cpp
index d6d99a0..91d07ab 100644
--- a/tests/sys_resource_test.cpp
+++ b/tests/sys_resource_test.cpp
@@ -18,17 +18,6 @@
 
 #include <sys/resource.h>
 
-#if defined(__GLIBC__)
-/* The host glibc we're currently building with doesn't have prlimit64 yet. */
-static int prlimit64(pid_t, int resource, const struct rlimit64* new_limit, struct rlimit64* old_limit) {
-  if (new_limit != NULL) {
-    return setrlimit64(resource, new_limit);
-  } else {
-    return getrlimit64(resource, old_limit);
-  }
-}
-#endif
-
 TEST(sys_resource, smoke) {
 #if defined(__LP64__) || defined(__GLIBC__)
   ASSERT_EQ(sizeof(rlimit), sizeof(rlimit64));
diff --git a/tests/unistd_test.cpp b/tests/unistd_test.cpp
index 19d4017..c9d9943 100644
--- a/tests/unistd_test.cpp
+++ b/tests/unistd_test.cpp
@@ -29,7 +29,6 @@
 #include <sys/wait.h>
 #include <unistd.h>
 
-
 TEST(unistd, sysconf_SC_MONOTONIC_CLOCK) {
   ASSERT_GT(sysconf(_SC_MONOTONIC_CLOCK), 0);
 }
@@ -250,8 +249,6 @@
 }
 
 TEST(unistd, unsetenv_EINVAL) {
-  EXPECT_EQ(-1, unsetenv(NULL));
-  EXPECT_EQ(EINVAL, errno);
   EXPECT_EQ(-1, unsetenv(""));
   EXPECT_EQ(EINVAL, errno);
   EXPECT_EQ(-1, unsetenv("a=b"));