diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 77cd8f3..15ae672 100644
*** a/src/backend/port/sysv_shmem.c
--- b/src/backend/port/sysv_shmem.c
*************** static void *
*** 102,109 ****
--- 102,129 ----
  InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
  {
  	IpcMemoryId shmid;
+ 	void	   *requestedAddress = NULL;
  	void	   *memAddress;
  
+ 	/*
+ 	 * Normally we just pass requestedAddress = NULL to shmat(), allowing the
+ 	 * system to choose where the segment gets mapped.  But in an EXEC_BACKEND
+ 	 * build, it's possible for whatever is chosen in the postmaster to not
+ 	 * work for backends, due to variations in address space layout.  As a
+ 	 * rather klugy workaround, allow the user to specify the address to use
+ 	 * via setting the environment variable PG_SHMEM_ADDR.  (If this were of
+ 	 * interest for anything except debugging, we'd probably create a cleaner
+ 	 * and better-documented way to set it, such as a GUC.)
+ 	 */
+ #ifdef EXEC_BACKEND
+ 	{
+ 		char	   *pg_shmem_addr = getenv("PG_SHMEM_ADDR");
+ 
+ 		if (pg_shmem_addr)
+ 			requestedAddress = (void *) strtoul(pg_shmem_addr, NULL, 0);
+ 	}
+ #endif
+ 
  	shmid = shmget(memKey, size, IPC_CREAT | IPC_EXCL | IPCProtection);
  
  	if (shmid < 0)
*************** InternalIpcMemoryCreate(IpcMemoryKey mem
*** 203,209 ****
  	on_shmem_exit(IpcMemoryDelete, Int32GetDatum(shmid));
  
  	/* OK, should be able to attach to the segment */
! 	memAddress = shmat(shmid, NULL, PG_SHMAT_FLAGS);
  
  	if (memAddress == (void *) -1)
  		elog(FATAL, "shmat(id=%d) failed: %m", shmid);
--- 223,229 ----
  	on_shmem_exit(IpcMemoryDelete, Int32GetDatum(shmid));
  
  	/* OK, should be able to attach to the segment */
! 	memAddress = shmat(shmid, requestedAddress, PG_SHMAT_FLAGS);
  
  	if (memAddress == (void *) -1)
  		elog(FATAL, "shmat(id=%d) failed: %m", shmid);