Index: lib/sanitizer_common/sanitizer_mac.cc
===================================================================
--- lib/sanitizer_common/sanitizer_mac.cc
+++ lib/sanitizer_common/sanitizer_mac.cc
@@ -93,20 +93,24 @@
 
 #include "sanitizer_syscall_generic.inc"
 
-// Direct syscalls, don't call libmalloc hooks.
+// Direct syscalls, don't call libmalloc hooks (but not available one 10.6).
 extern "C" void *__mmap(void *addr, size_t len, int prot, int flags, int fildes,
-                        off_t off);
-extern "C" int __munmap(void *, size_t);
+                        off_t off) SANITIZER_WEAK_ATTRIBUTE;
+extern "C" int __munmap(void *, size_t) SANITIZER_WEAK_ATTRIBUTE;
 
 // ---------------------- sanitizer_libc.h
 uptr internal_mmap(void *addr, size_t length, int prot, int flags,
                    int fd, u64 offset) {
   if (fd == -1) fd = VM_MAKE_TAG(VM_MEMORY_ANALYSIS_TOOL);
-  return (uptr)__mmap(addr, length, prot, flags, fd, offset);
+  if (__mmap)
+     return (uptr)__mmap(addr, length, prot, flags, fd, offset);
+  return (uptr) mmap(addr, length, prot, flags, fd, offset);
 }
 
 uptr internal_munmap(void *addr, uptr length) {
-  return __munmap(addr, length);
+  if (__munmap)
+    return __munmap(addr, length);
+  return munmap(addr, length);
 }
 
 int internal_mprotect(void *addr, uptr length, int prot) {
@@ -192,17 +196,19 @@
   return sigprocmask(how, set, oldset);
 }
 
-// Doesn't call pthread_atfork() handlers.
-extern "C" pid_t __fork(void);
+ // Doesn't call pthread_atfork() handlers (but not available on 10.6).
+extern "C" pid_t __fork(void) SANITIZER_WEAK_ATTRIBUTE;
 
 int internal_fork() {
-  return __fork();
+  if (__fork)
+    return __fork();
+  return fork();
 }
 
 int internal_forkpty(int *amaster) {
   int master, slave;
   if (openpty(&master, &slave, nullptr, nullptr, nullptr) == -1) return -1;
-  int pid = __fork();
+  int pid = internal_fork();
   if (pid == -1) {
     close(master);
     close(slave);
Index: lib/sanitizer_common/sanitizer_platform_interceptors.h
===================================================================
--- lib/sanitizer_common/sanitizer_platform_interceptors.h
+++ lib/sanitizer_common/sanitizer_platform_interceptors.h
@@ -47,9 +47,17 @@
 # define SI_LINUX 0
 #endif
 
+// FIXME: enable memmem on Windows.
+# define SI_MEMMEM SI_NOT_WINDOWS
+
 #if SANITIZER_MAC
 # define SI_MAC 1
 # define SI_NOT_MAC 0
+# if defined (__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) && \
+     __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 1070
+# undef SI_MEMMEM
+# define SI_MEMMEM 0
+# endif
 #else
 # define SI_MAC 0
 # define SI_NOT_MAC 1
@@ -83,8 +91,7 @@
 #define SANITIZER_INTERCEPT_MEMMOVE 1
 #define SANITIZER_INTERCEPT_MEMCPY 1
 #define SANITIZER_INTERCEPT_MEMCMP 1
-// FIXME: enable memmem on Windows.
-#define SANITIZER_INTERCEPT_MEMMEM SI_NOT_WINDOWS
+#define SANITIZER_INTERCEPT_MEMMEM SI_MEMMEM
 #define SANITIZER_INTERCEPT_MEMCHR 1
 #define SANITIZER_INTERCEPT_MEMRCHR SI_FREEBSD || SI_LINUX