diff -u pgsql.orig/src/backend/storage/ipc/shmem.c pgsql/src/backend/storage/ipc/shmem.c
--- pgsql.orig/src/backend/storage/ipc/shmem.c	2003-09-20 20:17:08.000000000 +0200
+++ pgsql/src/backend/storage/ipc/shmem.c	2003-09-20 20:34:21.000000000 +0200
@@ -131,6 +131,7 @@
 void *
 ShmemAlloc(Size size)
 {
+	uint32		newStart;
 	uint32		newFree;
 	void	   *newSpace;
 
@@ -146,10 +147,21 @@
 
 	SpinLockAcquire(ShmemLock);
 
-	newFree = shmemseghdr->freeoffset + size;
+	newStart = shmemseghdr->freeoffset;
+	if (size >= BLCKSZ)
+	{
+		/* Align BLCKSZ sized buffers even further:
+		 * - the costs are small
+		 * - some cpus (most notably Intel Pentium III)
+		 *   prefer well-aligned addresses for memory copies
+		 */
+		newStart = TYPEALIGN(32, newStart);
+	}
+
+	newFree = newStart + size;
 	if (newFree <= shmemseghdr->totalsize)
 	{
-		newSpace = (void *) MAKE_PTR(shmemseghdr->freeoffset);
+		newSpace = (void *) MAKE_PTR(newStart);
 		shmemseghdr->freeoffset = newFree;
 	}
 	else