diff --git a/src/backend/storage/aio/aio_io.c b/src/backend/storage/aio/aio_io.c
index 4d31392ddc7..00e176135a6 100644
--- a/src/backend/storage/aio/aio_io.c
+++ b/src/backend/storage/aio/aio_io.c
@@ -210,3 +210,26 @@ pgaio_io_uses_fd(PgAioHandle *ioh, int fd)
 
 	return false;				/* silence compiler */
 }
+
+/*
+ * Return the iovec and its length. Currently only expected to be used by
+ * debugging infrastructure
+ */
+int
+pgaio_io_get_iovec_length(PgAioHandle *ioh, struct iovec **iov)
+{
+	Assert(ioh->state >= PGAIO_HS_DEFINED);
+
+	*iov = &pgaio_ctl->iovecs[ioh->iovec_off];
+
+	switch (ioh->op)
+	{
+		case PGAIO_OP_READV:
+			return ioh->op_data.read.iov_length;
+		case PGAIO_OP_WRITEV:
+			return ioh->op_data.write.iov_length;
+		default:
+			pg_unreachable();
+			return 0;
+	}
+}
diff --git a/src/backend/storage/aio/method_worker.c b/src/backend/storage/aio/method_worker.c
index 31d94ac82c5..8ad17ec1ef7 100644
--- a/src/backend/storage/aio/method_worker.c
+++ b/src/backend/storage/aio/method_worker.c
@@ -42,6 +42,7 @@
 #include "storage/latch.h"
 #include "storage/proc.h"
 #include "tcop/tcopprot.h"
+#include "utils/memdebug.h"
 #include "utils/ps_status.h"
 #include "utils/wait_event.h"
 
@@ -529,6 +530,24 @@ IoWorkerMain(const void *startup_data, size_t startup_data_len)
 			error_errno = 0;
 			error_ioh = NULL;
 
+			/*
+			 * As part of IO completion the buffer will be marked as NOACCESS,
+			 * until the buffer is pinned again - which never happens in io
+			 * workers. Therefore the next time there is IO for the same
+			 * buffer, the memory will be considered inaccessible. To avoid
+			 * that, explicitly allow access to the memory before reading data
+			 * into it.
+			 */
+#ifdef USE_VALGRIND
+			{
+				struct iovec *iov;
+				uint16		iov_length = pgaio_io_get_iovec_length(ioh, &iov);
+
+				for (int i = 0; i < iov_length; i++)
+					VALGRIND_MAKE_MEM_UNDEFINED(iov[i].iov_base, iov[i].iov_len);
+			}
+#endif
+
 			/*
 			 * We don't expect this to ever fail with ERROR or FATAL, no need
 			 * to keep error_ioh set to the IO.
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 5da121872f4..941d7fa3d94 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -6881,6 +6881,19 @@ buffer_readv_complete_one(PgAioTargetData *td, uint8 buf_off, Buffer buffer,
 	/* Check for garbage data. */
 	if (!failed)
 	{
+		/*
+		 * If the buffer is not currently pinned by this backend, e.g. because
+		 * we're completing this IO after an error, the buffer data will have
+		 * been marked as inaccessible when the buffer was unpinned. The AIO
+		 * subsystem holds a pin, but that doesn't prevent the buffer from
+		 * having been marked as inaccessible. The completion might also be
+		 * executed in a different process.
+		 */
+#ifdef USE_VALGRIND
+		if (!BufferIsPinned(buffer))
+			VALGRIND_MAKE_MEM_DEFINED(bufdata, BLCKSZ);
+#endif
+
 		if (!PageIsVerified((Page) bufdata, tag.blockNum, piv_flags,
 							failed_checksum))
 		{
@@ -6899,6 +6912,12 @@ buffer_readv_complete_one(PgAioTargetData *td, uint8 buf_off, Buffer buffer,
 		else if (*failed_checksum)
 			*ignored_checksum = true;
 
+		/* undo what we did above */
+#ifdef USE_VALGRIND
+		if (!BufferIsPinned(buffer))
+			VALGRIND_MAKE_MEM_NOACCESS(bufdata, BLCKSZ);
+#endif
+
 		/*
 		 * Immediately log a message about the invalid page, but only to the
 		 * server log. The reason to do so immediately is that this may be
diff --git a/src/backend/storage/smgr/smgr.c b/src/backend/storage/smgr/smgr.c
index 4540284f581..bce37a36d51 100644
--- a/src/backend/storage/smgr/smgr.c
+++ b/src/backend/storage/smgr/smgr.c
@@ -746,6 +746,8 @@ smgrreadv(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
  *   responsible for pgaio_result_report() to mirror that news to the user (if
  *   the IO results in PGAIO_RS_WARNING) or abort the (sub)transaction (if
  *   PGAIO_RS_ERROR).
+ * - Under Valgrind, the "buffers" memory may or may not change status to
+ *   DEFINED, depending on io_method and concurrent activity.
  */
 void
 smgrstartreadv(PgAioHandle *ioh,
diff --git a/src/include/storage/aio_internal.h b/src/include/storage/aio_internal.h
index 7f18da2c856..33f27b9fe50 100644
--- a/src/include/storage/aio_internal.h
+++ b/src/include/storage/aio_internal.h
@@ -344,6 +344,7 @@ extern PgAioResult pgaio_io_call_complete_local(PgAioHandle *ioh);
 extern void pgaio_io_perform_synchronously(PgAioHandle *ioh);
 extern const char *pgaio_io_get_op_name(PgAioHandle *ioh);
 extern bool pgaio_io_uses_fd(PgAioHandle *ioh, int fd);
+extern int	pgaio_io_get_iovec_length(PgAioHandle *ioh, struct iovec **iov);
 
 /* aio_target.c */
 extern bool pgaio_io_can_reopen(PgAioHandle *ioh);