diff --git a/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.pass.cpp b/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.pass.cpp
--- a/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.pass.cpp
+++ b/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.pass.cpp
@@ -10732,7 +10732,8 @@
     std::string nan= "nan";
     std::string NaN = "NAN";
     std::string nan_padding25 = "**********************";
-#if defined(TEST_HAS_GLIBC) || defined(_WIN32)
+#if defined(TEST_HAS_GLIBC) || defined(_WIN32) || \
+        (defined(__BIONIC__) && !defined(ANDROID_PRINTF_NAN_NO_SIGN))
     std::string pnan_sign = "+";
     std::string pnan_padding25 = "*********************";
 #else
diff --git a/libcxx/test/std/localization/locale.categories/category.numeric/locale.num.get/facet.num.get.members/get_long_double.pass.cpp b/libcxx/test/std/localization/locale.categories/category.numeric/locale.num.get/facet.num.get.members/get_long_double.pass.cpp
--- a/libcxx/test/std/localization/locale.categories/category.numeric/locale.num.get/facet.num.get.members/get_long_double.pass.cpp
+++ b/libcxx/test/std/localization/locale.categories/category.numeric/locale.num.get/facet.num.get.members/get_long_double.pass.cpp
@@ -145,6 +145,7 @@
         assert(err == ios.goodbit);
         assert(v == -INFINITY);
     }
+#ifndef ANDROID_BROKEN_STRTOLD_NAN
     {
         const char str[] = "nan";
         std::hex(ios);
@@ -169,6 +170,7 @@
         assert(err == ios.goodbit);
         assert(std::isnan(v));
     }
+#endif // ANDROID_BROKEN_STRTOLD_NAN
     {
         const char str[] = "1.189731495357231765021264e+49321";
         std::ios_base::iostate err = ios.goodbit;
diff --git a/libcxx/test/std/strings/string.conversions/stold.pass.cpp b/libcxx/test/std/strings/string.conversions/stold.pass.cpp
--- a/libcxx/test/std/strings/string.conversions/stold.pass.cpp
+++ b/libcxx/test/std/strings/string.conversions/stold.pass.cpp
@@ -39,11 +39,13 @@
         assert(std::stold("INF", &idx) == INFINITY);
         assert(idx == 3);
     }
+#ifndef ANDROID_BROKEN_STRTOLD_NAN
     {
         size_t idx = 0;
         assert(std::isnan(std::stold("NAN", &idx)));
         assert(idx == 3);
     }
+#endif
 
 #ifndef TEST_HAS_NO_EXCEPTIONS
     {
@@ -104,11 +106,13 @@
         assert(std::stold(L"INF", &idx) == INFINITY);
         assert(idx == 3);
     }
+#ifndef ANDROID_BROKEN_STRTOLD_NAN
     {
         size_t idx = 0;
         assert(std::isnan(std::stold(L"NAN", &idx)));
         assert(idx == 3);
     }
+#endif
 #ifndef TEST_HAS_NO_EXCEPTIONS
     {
         size_t idx = 0;
diff --git a/libcxx/utils/libcxx/test/features.py b/libcxx/utils/libcxx/test/features.py
--- a/libcxx/utils/libcxx/test/features.py
+++ b/libcxx/utils/libcxx/test/features.py
@@ -146,6 +146,56 @@
             }
           """)),
 
+  # For Android, some of libc++'s floating-point conversions are implemented
+  # using Bionic (libc.so) on the device, which has bugs and behavioral
+  # differences on older OS versions. We want to adjust test behavior using the
+  # device version, not __ANDROID_API__, because it is useful/interesting to
+  # build test programs against an old Android API level and run them on a new
+  # Android OS.
+
+  # printf's output for NAN has changed between versions of Android. Considering
+  # NAN and -NAN:
+  #  - Android L (APIs 21 and 22): "%f" and "%+f" print "nan".
+  #  - Android M (API 23) and up: "%f" prints "nan" or "-nan", "%+f" prints
+  #    "+nan" or "-nan".
+  # Set this feature for L, where the sign is never printed.
+  Feature(name='android-printf-nan-no-sign',
+          when=lambda cfg: '__ANDROID__' in compilerMacros(cfg) and not programSucceeds(cfg, """
+            #include <android/api-level.h>
+            #include <math.h>
+            #include <stdio.h>
+            int main(int, char**) {
+              // Never enable the workaround on Android M or newer.
+              if (android_get_device_api_level() >= 23) return 0;
+              char buf[100];
+              snprintf(buf, sizeof(buf), "%+f", NAN);
+              return buf[0] != '+';
+            }
+          """),
+          actions=[AddCompileFlag('-DANDROID_PRINTF_NAN_NO_SIGN')]),
+
+  # strtold does not handle "NAN" correctly on 64-bit Android prior to Android O
+  # (API 26). (It produces 0.0 instead of NAN.) Set a macro when the device's
+  # strtold is broken.
+  # See https://android-review.googlesource.com/q/Id7d46ac2d8acb8770b5e8c445e87cfabfde6f111.
+  Feature(name='android-broken-strtold-nan',
+          when=lambda cfg: '__ANDROID__' in compilerMacros(cfg) and not programSucceeds(cfg, """
+            #include <android/api-level.h>
+            #include <math.h>
+            int main(int, char**) {
+              // Never enable the workaround on Android O or newer, or on
+              // unaffected architectures.
+            #if defined(__LP64__)
+              if (android_get_device_api_level() >= 26) return 0;
+              long double result = strtold("NAN", NULL);
+              return !isnan(result);
+            #else
+              return 0;
+            #endif
+            }
+          """),
+          actions=[AddCompileFlag('-DANDROID_BROKEN_STRTOLD_NAN')]),
+
   # Whether Bash can run on the executor.
   # This is not always the case, for example when running on embedded systems.
   #