Index: lib/sanitizer_common/sanitizer_common_interceptors.inc
===================================================================
--- lib/sanitizer_common/sanitizer_common_interceptors.inc
+++ lib/sanitizer_common/sanitizer_common_interceptors.inc
@@ -226,11 +226,10 @@
 #ifndef COMMON_INTERCEPTOR_STRNDUP_IMPL
 #define COMMON_INTERCEPTOR_STRNDUP_IMPL(ctx, s, size)                          \
   COMMON_INTERCEPTOR_ENTER(ctx, strndup, s, size);                             \
-  uptr from_length = internal_strnlen(s, size);                                \
-  uptr copy_length = Min(size, from_length);                                   \
+  uptr copy_length = internal_strnlen(s, size);                                \
   char *new_mem = (char *)WRAP(malloc)(copy_length + 1);                       \
   if (common_flags()->intercept_strndup) {                                     \
-    COMMON_INTERCEPTOR_READ_RANGE(ctx, s, copy_length + 1);                    \
+    COMMON_INTERCEPTOR_READ_STRING(ctx, s, Min(size, copy_length + 1));        \
   }                                                                            \
   COMMON_INTERCEPTOR_COPY_STRING(ctx, new_mem, s, copy_length);                \
   internal_memcpy(new_mem, s, copy_length);                                    \
Index: test/asan/TestCases/Posix/strndup_no_null_test.cc
===================================================================
--- /dev/null
+++ test/asan/TestCases/Posix/strndup_no_null_test.cc
@@ -0,0 +1,22 @@
+// RUN: %clang_asan -O0 %s -o %t && not %run %t 2>&1 | FileCheck %s
+// RUN: %clang_asan -O1 %s -o %t && not %run %t 2>&1 | FileCheck %s
+// RUN: %clang_asan -O2 %s -o %t && not %run %t 2>&1 | FileCheck %s
+// RUN: %clang_asan -O3 %s -o %t && not %run %t 2>&1 | FileCheck %s
+
+// When built as C on Linux, strndup is transformed to __strndup.
+// RUN: %clang_asan -O3 -xc %s -o %t && not %run %t 2>&1 | FileCheck %s
+
+// Unwind problem on arm: "main" is missing from the allocation stack trace.
+// UNSUPPORTED: win32,s390,armv7l-unknown-linux-gnueabihf
+
+#include <string.h>
+
+char kChars[] = {'f', 'o', 'o'};
+
+int main(int argc, char **argv) {
+  char *copy = strndup(kChars, 3);
+  copy = strndup(kChars, 10);
+  // CHECK: AddressSanitizer: global-buffer-overflow
+  // CHECK: {{.*}}main {{.*}}strndup_no_null_test.cc:[[@LINE-2]]
+  return *copy;
+}