diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index bda475a719..3df73542e1 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -3456,6 +3456,24 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length)
              * so a userfault will trigger.
              */
 #ifdef CONFIG_FALLOCATE_PUNCH_HOLE
+            /*
+             * We'll discard data from the actual file, even though we only
+             * have a MAP_PRIVATE mapping, possibly messing with other
+             * MAP_PRIVATE/MAP_SHARED mappings. There is no easy way to
+             * change that behavior whithout violating the promised
+             * semantics of ram_block_discard_range().
+             *
+             * Only warn, because it works as long as nobody else uses that
+             * file.
+             */
+            if (!qemu_ram_is_shared(rb)) {
+                warn_report_once("ram_block_discard_range: Discarding RAM"
+                                 " in private file mappings is possibly"
+                                 " dangerous, because it will modify the"
+                                 " underlying file and will affect other"
+                                 " users of the file");
+            }
+
             ret = fallocate(rb->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
                             start, length);
             if (ret) {