diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index fbc05f0dc13..c9a9b7ec66c 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -925,7 +925,14 @@ ShmemResizeStruct(const char *name, Size new_size)
 	new_end = (char *) TYPEALIGN(page_size, (char *) result->location + new_size);
 	if (new_size < result->size)
 	{
-		char	   *max_end = (char *) TYPEALIGN_DOWN(page_size, (char *) result->location + result->maximum_size);
+		/*
+		 * Only pages currently RW should be freed; anything past result->size
+		 * is PROT_NONE reserved tail.  Also stop before the last page shared
+		 * with the next structure.
+		 */
+		char	   *current_end = (char *) TYPEALIGN(page_size, (char *) result->location + result->size);
+		char	   *reserved_end = (char *) TYPEALIGN_DOWN(page_size, (char *) result->location + result->maximum_size);
+		char	   *max_end = Min(current_end, reserved_end);
 
 		if (max_end > new_end)
 		{