diff --git a/compiler-rt/lib/asan/asan_interceptors.cc b/compiler-rt/lib/asan/asan_interceptors.cc
index 5cbf3f3e6dc5..81d261ef9e4f 100644
--- a/compiler-rt/lib/asan/asan_interceptors.cc
+++ b/compiler-rt/lib/asan/asan_interceptors.cc
@@ -43,24 +43,25 @@
 // After interception, the calls to system functions will be substituted by
 // calls to our interceptors. We store pointers to system function f()
 // in __asan::real_f().
-//
-// TODO(glider): mach_override_ptr() tends to spend too much time
-// in allocateBranchIsland(). This should be ok for real-word
-// application, but slows down our tests which fork too many children.
 #ifdef __APPLE__
 #include "mach_override/mach_override.h"
 #define WRAPPER_NAME(x) "wrap_"#x
 
-#define OVERRIDE_FUNCTION(oldfunc, newfunc)                             \
-  CHECK(0 == __asan_mach_override_ptr((void*)(oldfunc),                        \
-                                      (void*)(newfunc),                        \
-                                      (void**)&real_##oldfunc));               \
-  CHECK(real_##oldfunc != NULL);
+#define OVERRIDE_FUNCTION(oldfunc, newfunc)                                   \
+  do {CHECK(0 == __asan_mach_override_ptr_custom((void*)(oldfunc),            \
+                                                 (void*)(newfunc),            \
+                                                 (void**)&real_##oldfunc,     \
+                                                 __asan_allocate_island,      \
+                                                 __asan_deallocate_island));  \
+  CHECK(real_##oldfunc != NULL);   } while(0)
 
-#define OVERRIDE_FUNCTION_IF_EXISTS(oldfunc, newfunc)                   \
-  do { __asan_mach_override_ptr((void*)(oldfunc),                              \
-                                (void*)(newfunc),                              \
-                                (void**)&real_##oldfunc); } while (0)
+#define OVERRIDE_FUNCTION_IF_EXISTS(oldfunc, newfunc)               \
+  do { __asan_mach_override_ptr_custom((void*)(oldfunc),            \
+                                       (void*)(newfunc),            \
+                                       (void**)&real_##oldfunc,     \
+                                       __asan_allocate_island,      \
+                                       __asan_deallocate_island);   \
+  } while (0)
 
 #define INTERCEPT_FUNCTION(func)                                        \
   OVERRIDE_FUNCTION(func, WRAP(func))
diff --git a/compiler-rt/lib/asan/asan_mac.cc b/compiler-rt/lib/asan/asan_mac.cc
index 4bfe74cb4877..0bf978214b82 100644
--- a/compiler-rt/lib/asan/asan_mac.cc
+++ b/compiler-rt/lib/asan/asan_mac.cc
@@ -32,6 +32,8 @@
 
 namespace __asan {
 
+void *island_allocator_pos = NULL;
+
 extern dispatch_async_f_f real_dispatch_async_f;
 extern dispatch_sync_f_f real_dispatch_sync_f;
 extern dispatch_after_f_f real_dispatch_after_f;
@@ -172,6 +174,37 @@ void AsanLock::Unlock() {
   OSSpinLockUnlock((OSSpinLock*)&opaque_storage_);
 }
 
+// The range of pages to be used by __asan_mach_override_ptr for escape
+// islands.
+// TODO(glider): instead of mapping a fixed range we must find a range of
+// unmapped pages in vmmap and take them.
+#define kIslandEnd (0x7fffffdf0000 - kPageSize)
+#define kIslandBeg (kIslandEnd - 256 * kPageSize)
+
+extern "C"
+mach_error_t __asan_allocate_island(void **ptr,
+                                    size_t unused_size,
+                                    void *unused_hint) {
+  if (!island_allocator_pos) {
+    if ((void*)-1 == asan_mmap((void*)kIslandBeg, kIslandEnd - kIslandBeg,
+                               PROT_READ | PROT_WRITE | PROT_EXEC,
+                               MAP_PRIVATE | MAP_ANON | MAP_FIXED,
+                               -1, 0)) {
+      return KERN_NO_SPACE;
+    }
+    island_allocator_pos = (void*)kIslandBeg;
+  };
+  *ptr = island_allocator_pos;
+  island_allocator_pos = (char*)island_allocator_pos + kPageSize;
+  return err_none;
+}
+
+extern "C"
+mach_error_t __asan_deallocate_island(void *ptr) {
+  // Do nothing.
+  // TODO(glider): allow to free and reuse the island memory.
+  return err_none;
+}
 
 // Support for the following functions from libdispatch on Mac OS:
 //   dispatch_async_f()
diff --git a/compiler-rt/lib/asan/asan_mac.h b/compiler-rt/lib/asan/asan_mac.h
index 32739e766cc7..7c941f81b837 100644
--- a/compiler-rt/lib/asan/asan_mac.h
+++ b/compiler-rt/lib/asan/asan_mac.h
@@ -20,6 +20,7 @@
 
 // TODO(glider): need to check if the OS X version is 10.6 or greater.
 #include <dispatch/dispatch.h>
+#include <mach/mach_error.h>
 #include <setjmp.h>
 
 typedef void* pthread_workqueue_t;
@@ -54,6 +55,15 @@ typedef struct {
 
 
 extern "C" {
+
+// Allocate memory for the escape island. This cannot be moved to
+// mach_override, because the allocator needs to know about the ASan shadow
+// mappings.
+// TODO(glider): in order to place a relative jump the allocated memory should
+// be within 2 Gb from the hint address.
+mach_error_t __asan_allocate_island(void **ptr, size_t unused_size, void *unused_hint);
+mach_error_t __asan_deallocate_island(void *ptr);
+
 // dispatch_barrier_async_f() is not declared in <dispatch/dispatch.h>.
 void dispatch_barrier_async_f(dispatch_queue_t dq,
                               void *ctxt, dispatch_function_t func);