diff --git a/docs/tracing.txt b/docs/tracing.txt
index ae01ff1378..5504850857 100644
--- a/docs/tracing.txt
+++ b/docs/tracing.txt
@@ -72,6 +72,10 @@ Trace events should use types as follows:
  * For everything else, use primitive scalar types (char, int, long) with the
    appropriate signedness.
 
+Format strings should reflect the types defined in the trace event.  Take
+special care to use PRId64 and PRIu64 for int64_t and uint64_t types,
+respectively.  This ensures portability between 32- and 64-bit platforms.
+
 === Hints for adding new trace events ===
 
 1. Trace state changes in the code.  Interesting points in the code usually
diff --git a/trace-events b/trace-events
index f32c83fa26..b43317e914 100644
--- a/trace-events
+++ b/trace-events
@@ -55,10 +55,10 @@ disable bdrv_aio_multiwrite_latefail(void *mcb, int i) "mcb %p i %d"
 # hw/virtio-blk.c
 disable virtio_blk_req_complete(void *req, int status) "req %p status %d"
 disable virtio_blk_rw_complete(void *req, int ret) "req %p ret %d"
-disable virtio_blk_handle_write(void *req, unsigned long sector, unsigned long nsectors) "req %p sector %lu nsectors %lu"
+disable virtio_blk_handle_write(void *req, uint64_t sector, size_t nsectors) "req %p sector %"PRIu64" nsectors %zu"
 
 # posix-aio-compat.c
-disable paio_submit(void *acb, void *opaque, unsigned long sector_num, unsigned long nb_sectors, unsigned long type) "acb %p opaque %p sector_num %lu nb_sectors %lu type %lu"
+disable paio_submit(void *acb, void *opaque, int64_t sector_num, int nb_sectors, int type) "acb %p opaque %p sector_num %"PRId64" nb_sectors %d type %d"
 
 # ioport.c
 disable cpu_in(unsigned int addr, unsigned int val) "addr %#x value %u"