diff --git a/src/widgets/widgets/qmdiarea.cpp b/src/widgets/widgets/qmdiarea.cpp
index fdb3e6a1074..93de95547e7 100644
--- a/src/widgets/widgets/qmdiarea.cpp
+++ b/src/widgets/widgets/qmdiarea.cpp
@@ -2343,7 +2343,12 @@ void QMdiArea::showEvent(QShowEvent *showEvent)
     }
 
     if (!d->pendingPlacements.isEmpty()) {
-        foreach (QMdiSubWindow *window, d->pendingPlacements) {
+        // Nothing obvious in the loop body changes the container (in this code path)
+        // during iteration, this is calling into a non-const method that does change
+        // the container when called from other places. So take a copy anyway for good
+        // measure.
+        const auto copy = d->pendingPlacements;
+        for (QMdiSubWindow *window : copy) {
             if (!window)
                 continue;
             if (!window->testAttribute(Qt::WA_Resized)) {