diff --git a/libc/include/string.h b/libc/include/string.h
index 56d89a4..02d8151 100644
--- a/libc/include/string.h
+++ b/libc/include/string.h
@@ -119,9 +119,16 @@
     return __builtin___strcpy_chk(dest, src, __builtin_object_size (dest, 0));
 }
 
+extern void __strncpy_error()
+    __attribute__((__error__("strncpy called with size bigger than buffer")));
+
 __BIONIC_FORTIFY_INLINE
 char *strncpy(char *dest, const char *src, size_t n) {
-    return __builtin___strncpy_chk(dest, src, n, __builtin_object_size (dest, 0));
+    size_t bos = __bos(dest);
+    if (__builtin_constant_p(n) && (n > bos)) {
+        __strncpy_error();
+    }
+    return __builtin___strncpy_chk(dest, src, n, bos);
 }
 
 __BIONIC_FORTIFY_INLINE
diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 1976d6a..1288b28 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -517,6 +517,12 @@
 
 #if defined(_FORTIFY_SOURCE) && _FORTIFY_SOURCE > 0 && defined(__OPTIMIZE__) && __OPTIMIZE__ > 0 && !defined(__clang__)
 #define __BIONIC_FORTIFY 1
+#if _FORTIFY_SOURCE == 2
+#define __bos(s) __builtin_object_size((s), 1);
+#else
+#define __bos(s) __builtin_object_size((s), 0);
+#endif
+
 #define __BIONIC_FORTIFY_INLINE \
     extern inline \
     __attribute__ ((always_inline)) \
diff --git a/tests/Android.mk b/tests/Android.mk
index dee5e33..45cb462 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -60,6 +60,8 @@
     dirent_test.cpp \
     eventfd_test.cpp \
     fenv_test.cpp \
+    fortify1_test.cpp \
+    fortify2_test.cpp \
     getauxval_test.cpp \
     getcwd_test.cpp \
     libc_logging_test.cpp \
diff --git a/tests/fortify1_test.cpp b/tests/fortify1_test.cpp
new file mode 100644
index 0000000..0cbb8cf
--- /dev/null
+++ b/tests/fortify1_test.cpp
@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2013 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 _FORTIFY_SOURCE
+#define _FORTIFY_SOURCE 1
+
+#include <gtest/gtest.h>
+#include <string.h>
+
+#if __BIONIC__
+// We have to say "DeathTest" here so gtest knows to run this test (which exits)
+// in its own process.
+TEST(Fortify1_DeathTest, strcpy_fortified) {
+  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
+  char buf[10];
+  char *orig = strdup("0123456789");
+  ASSERT_EXIT(strcpy(buf, orig), testing::KilledBySignal(SIGSEGV), "");
+  free(orig);
+}
+
+TEST(Fortify1_DeathTest, strlen_fortified) {
+  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
+  char buf[10];
+  memcpy(buf, "0123456789", sizeof(buf));
+  ASSERT_EXIT(printf("%d", strlen(buf)), testing::KilledBySignal(SIGSEGV), "");
+}
+
+TEST(Fortify1_DeathTest, strchr_fortified) {
+  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
+  char buf[10];
+  memcpy(buf, "0123456789", sizeof(buf));
+  ASSERT_EXIT(printf("%s", strchr(buf, 'a')), testing::KilledBySignal(SIGSEGV), "");
+}
+
+TEST(Fortify1_DeathTest, strrchr_fortified) {
+  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
+  char buf[10];
+  memcpy(buf, "0123456789", sizeof(buf));
+  ASSERT_EXIT(printf("%s", strrchr(buf, 'a')), testing::KilledBySignal(SIGSEGV), "");
+}
+#endif
diff --git a/tests/fortify2_test.cpp b/tests/fortify2_test.cpp
new file mode 100644
index 0000000..9bedbe5
--- /dev/null
+++ b/tests/fortify2_test.cpp
@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2013 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 _FORTIFY_SOURCE
+#define _FORTIFY_SOURCE 2
+
+#include <gtest/gtest.h>
+#include <string.h>
+
+struct foo {
+  char a[10];
+  char b[10];
+};
+
+// We have to say "DeathTest" here so gtest knows to run this test (which exits)
+// in its own process.
+TEST(Fortify2_DeathTest, strncpy_fortified) {
+  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
+  foo myfoo;
+  int copy_amt = atoi("11");
+  ASSERT_EXIT(strncpy(myfoo.a, "01234567890", copy_amt),
+              testing::KilledBySignal(SIGSEGV), "");
+}
+
+#if __BIONIC__
+TEST(Fortify2_DeathTest, strcpy_fortified) {
+  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
+  char buf[10];
+  char *orig = strdup("0123456789");
+  ASSERT_EXIT(strcpy(buf, orig), testing::KilledBySignal(SIGSEGV), "");
+  free(orig);
+}
+
+TEST(Fortify2_DeathTest, strlen_fortified) {
+  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
+  char buf[10];
+  memcpy(buf, "0123456789", sizeof(buf));
+  ASSERT_EXIT(printf("%d", strlen(buf)), testing::KilledBySignal(SIGSEGV), "");
+}
+
+TEST(Fortify2_DeathTest, strchr_fortified) {
+  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
+  char buf[10];
+  memcpy(buf, "0123456789", sizeof(buf));
+  ASSERT_EXIT(printf("%s", strchr(buf, 'a')), testing::KilledBySignal(SIGSEGV), "");
+}
+
+TEST(Fortify2_DeathTest, strrchr_fortified) {
+  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
+  char buf[10];
+  memcpy(buf, "0123456789", sizeof(buf));
+  ASSERT_EXIT(printf("%s", strrchr(buf, 'a')), testing::KilledBySignal(SIGSEGV), "");
+}
+#endif
diff --git a/tests/string_test.cpp b/tests/string_test.cpp
index 1720058..eb10c16 100644
--- a/tests/string_test.cpp
+++ b/tests/string_test.cpp
@@ -307,39 +307,6 @@
 
 
 #if __BIONIC__
-// We have to say "DeathTest" here so gtest knows to run this test (which exits)
-// in its own process.
-TEST(string_DeathTest, strcpy_fortified) {
-  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
-  char buf[10];
-  char *orig = strdup("0123456789");
-  ASSERT_EXIT(strcpy(buf, orig), testing::KilledBySignal(SIGSEGV), "");
-  free(orig);
-}
-
-TEST(string_DeathTest, strlen_fortified) {
-  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
-  char buf[10];
-  memcpy(buf, "0123456789", sizeof(buf));
-  ASSERT_EXIT(printf("%d", strlen(buf)), testing::KilledBySignal(SIGSEGV), "");
-}
-
-TEST(string_DeathTest, strchr_fortified) {
-  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
-  char buf[10];
-  memcpy(buf, "0123456789", sizeof(buf));
-  ASSERT_EXIT(printf("%s", strchr(buf, 'a')), testing::KilledBySignal(SIGSEGV), "");
-}
-
-TEST(string_DeathTest, strrchr_fortified) {
-  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
-  char buf[10];
-  memcpy(buf, "0123456789", sizeof(buf));
-  ASSERT_EXIT(printf("%s", strrchr(buf, 'a')), testing::KilledBySignal(SIGSEGV), "");
-}
-#endif
-
-#if __BIONIC__
 TEST(string, strlcat) {
   StringTestState state(SMALL);
   for (size_t i = 0; i < state.n; i++) {