diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c
index fb44d75..3de13e7 100644
--- a/src/backend/storage/buffer/localbuf.c
+++ b/src/backend/storage/buffer/localbuf.c
@@ -813,7 +813,8 @@ PinLocalBuffer(BufferDesc *buf_hdr, bool adjust_usagecount)
 		pg_atomic_unlocked_write_u32(&buf_hdr->state, buf_state);
 
 		/* see comment in PinBuffer() */
-		VALGRIND_MAKE_MEM_DEFINED(LocalBufHdrGetBlock(buf_hdr), BLCKSZ);
+		if (LocalBufHdrGetBlock(bufHdr) != NULL)
+			VALGRIND_MAKE_MEM_DEFINED(LocalBufHdrGetBlock(buf_hdr), BLCKSZ);
 	}
 	LocalRefCount[bufid]++;
 	ResourceOwnerRememberBuffer(CurrentResourceOwner,
@@ -932,6 +933,15 @@ GetLocalBufferStorage(void)
 	next_buf_in_block++;
 	total_bufs_allocated++;
 
+	/*
+	 * Caller's PinBuffer() was too early for Valgrind updates, so do it here.
+	 * The block is actually undefined, but we want consistency with the
+	 * regular case of not needing to allocate memory.  This is specifically
+	 * needed when method_io_uring.c fills the block, because Valgrind doesn't
+	 * recognize io_uring reads causing undefined memory to become defined.
+	 */
+	VALGRIND_MAKE_MEM_DEFINED(this_buf, BLCKSZ);
+
 	return (Block) this_buf;
 }