diff --git a/winsup/cygwin/create_posix_thread.cc b/winsup/cygwin/create_posix_thread.cc
index 534600fd1..8e06099e4 100644
--- a/winsup/cygwin/create_posix_thread.cc
+++ b/winsup/cygwin/create_posix_thread.cc
@@ -107,10 +107,6 @@ pthread_wrapper (PVOID arg)
   api_fatal ("Dumb thinko in pthread handling.  Whip the developer.");
 }
 
-/* The memory region used for thread stacks. The memory layout is outlined
-   in heap.cc, function eval_start_address(). */
-#define THREAD_STORAGE_LOW	0x600000000L
-#define THREAD_STORAGE_HIGH	0x800000000L
 /* We provide the stacks always in 1 Megabyte slots */
 #define THREAD_STACK_SLOT	0x000100000L	/* 1 Meg */
 /* Maximum stack size returned from the pool. */
diff --git a/winsup/cygwin/local_includes/memory_layout.h b/winsup/cygwin/local_includes/memory_layout.h
new file mode 100644
index 000000000..77ab61984
--- /dev/null
+++ b/winsup/cygwin/local_includes/memory_layout.h
@@ -0,0 +1,59 @@
+/* memory_layout.h: document all addresses crucial to the fixed memory
+		    layout of Cygwin processes.
+
+This file is part of Cygwin.
+
+This software is a copyrighted work licensed under the terms of the
+Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
+details. */
+
+/* We use fixed addresses outside the low 32 bit arena, which is exclusively
+   used by the OS now:
+     - The executable starts at 0x1:00400000L
+     - The Cygwin DLL starts at 0x1:80040000L
+     - Rebased DLLs are located from 0x2:00000000L up to 0x4:00000000L
+     - auto-image-based DLLs are located from 0x4:00000000L up to 0x6:00000000L
+     - Thread stacks are located from 0x6:00000000L up to 0x8:00000000L.
+     - So the heap starts at 0x8:00000000L. */
+
+  /* TODO: Make Cygwin work with ASLR.
+     - The executable starts at 0x1:00400000L
+     - Rebased non-ASLRed DLLs from 0x2:00000000L up to 0x4:00000000L
+     - auto-image-based non-ASLRed DLLs from 0x4:00000000L up to 0x6:00000000L
+     - Thread stacks are located from 0x6:00000000L up to 0x8:00000000L.
+     - cygheap from 0x8:00000000L up to 0xa:00000000L.
+     - So the heap starts at 0xa:00000000L. */
+
+/* This is where the Cygwin executables are loaded to. */
+#define EXECUTABLE_ADDRESS		0x100400000UL
+
+/* Fixed address set by the linker. The Cygwin DLL will have this address set
+   in the DOS header. Keep this area free with ASLR, for the case where
+   dynamicbase is accidentally not set in the PE/COFF header of the DLL. */
+#define CYGWIN_DLL_ADDRESS		0x180040000UL
+
+/* Rebased DLLs are located in this 16 Gigs arena.  Will be kept for
+   backward compatibility. */
+#define REBASED_DLL_STORAGE_LOW		0x200000000UL
+#define REBASED_DLL_STORAGE_HIGH	0x400000000UL
+
+/* Auto-image-based DLLs are located in this 16 Gigs arena.  This is used
+   by the linker to set a default address for DLLs. */
+#define AUTOBASED_DLL_STORAGE_LOW	0x400000000UL
+#define AUTOBASED_DLL_STORAGE_HIGH	0x600000000UL
+
+/* Storage area for thread stacks. */
+#define THREAD_STORAGE_LOW		0x600000000UL
+#define THREAD_STORAGE_HIGH		0x800000000UL
+
+/* This is where the user heap starts.  There's no defined end address.
+   The user heap pontentially grows into the mmap arena.  However,
+   the user heap grows upwar4ds and the mmap arena grows downwards,
+   so there's not much chance to meet unluckily. */
+#define USERHEAP_START			0x800000000UL
+
+/* The memory region used for memory maps.
+   Up to Win 8 only 44 bit address space, 48 bit starting witrh 8.1, so
+   the max value is variable. */
+#define MMAP_STORAGE_LOW	0x001000000000L /* Leave ~32 Gigs for heap. */
+#define MMAP_STORAGE_HIGH       wincap.mmap_storage_high ()
diff --git a/winsup/cygwin/local_includes/mmap_alloc.h b/winsup/cygwin/local_includes/mmap_alloc.h
index 8d6aebcaf..86a42aee1 100644
--- a/winsup/cygwin/local_includes/mmap_alloc.h
+++ b/winsup/cygwin/local_includes/mmap_alloc.h
@@ -1,8 +1,4 @@
-/* The memory region used for memory maps */
-#define MMAP_STORAGE_LOW	0x001000000000L	/* Leave 32 Gigs for heap. */
-/* Up to Win 8 only supporting 44 bit address space, starting with Win 8.1
-   48 bit address space. */
-#define MMAP_STORAGE_HIGH	wincap.mmap_storage_high ()
+#include "memory_layout.h"
 
 class mmap_allocator
 {
diff --git a/winsup/cygwin/mm/heap.cc b/winsup/cygwin/mm/heap.cc
index 14c42e45c..5b24a197f 100644
--- a/winsup/cygwin/mm/heap.cc
+++ b/winsup/cygwin/mm/heap.cc
@@ -15,6 +15,7 @@ details. */
 #include "cygheap.h"
 #include "child_info.h"
 #include "ntdll.h"
+#include "memory_layout.h"
 #include <sys/param.h>
 
 #define assert(x)
@@ -26,21 +27,6 @@ static ptrdiff_t page_const;
 /* Chunksize of subsequent heap reservations. */
 #define RAISEHEAP_SIZE (1 * 1024 * 1024)
 
-static uintptr_t
-eval_start_address ()
-{
-  /* We choose a fixed address outside the low 32 bit arena, which is
-     exclusively used by the OS now:
-     - The executable starts at 0x1:00400000L
-     - The Cygwin DLL starts at 0x1:80040000L
-     - Rebased DLLs are located from 0x2:00000000L up to 0x4:00000000L
-     - auto-image-based DLLs are located from 0x4:00000000L up to 0x6:00000000L
-     - Thread stacks are located from 0x6:00000000L up to 0x8:00000000L.
-     - So the heap starts at 0x8:00000000L. */
-  uintptr_t start_address = 0x800000000L;
-  return start_address;
-}
-
 static SIZE_T
 eval_initial_heap_size ()
 {
@@ -77,7 +63,7 @@ user_heap_info::init ()
   page_const = wincap.page_size ();
   if (!base)
     {
-      uintptr_t start_address = eval_start_address ();
+      uintptr_t start_address = USERHEAP_START;
       PVOID largest_found = NULL;
       SIZE_T largest_found_size = 0;
       SIZE_T ret;