diff --git a/src/corelib/tools/qarraydata.h b/src/corelib/tools/qarraydata.h
index ae4cbc3081..78fbc9cf32 100644
--- a/src/corelib/tools/qarraydata.h
+++ b/src/corelib/tools/qarraydata.h
@@ -91,6 +91,13 @@ struct Q_CORE_EXPORT QArrayData
 
     Q_DECLARE_FLAGS(AllocationOptions, AllocationOption)
 
+    size_t detachCapacity(size_t newSize) const
+    {
+        if (capacityReserved && newSize < alloc)
+            return alloc;
+        return newSize;
+    }
+
     AllocationOptions detachFlags() const
     {
         AllocationOptions result;
diff --git a/src/corelib/tools/qarraydatapointer.h b/src/corelib/tools/qarraydatapointer.h
index f5ad53aa54..4eb90ac35e 100644
--- a/src/corelib/tools/qarraydatapointer.h
+++ b/src/corelib/tools/qarraydatapointer.h
@@ -171,7 +171,7 @@ public:
 private:
     Data *clone(QArrayData::AllocationOptions options) const Q_REQUIRED_RESULT
     {
-        QArrayDataPointer copy(Data::allocate(d->alloc ? d->alloc : d->size,
+        QArrayDataPointer copy(Data::allocate(d->detachCapacity(d->size),
                     options));
         if (d->size)
             copy->copyAppend(d->begin(), d->end());
diff --git a/tests/auto/corelib/tools/qarraydata/simplevector.h b/tests/auto/corelib/tools/qarraydata/simplevector.h
index 0cc7561b46..54c9fae589 100644
--- a/tests/auto/corelib/tools/qarraydata/simplevector.h
+++ b/tests/auto/corelib/tools/qarraydata/simplevector.h
@@ -184,7 +184,7 @@ public:
         if (d->ref.isShared()
                 || capacity() - size() < size_t(last - first)) {
             SimpleVector detached(Data::allocate(
-                        qMax(capacity(), size() + (last - first)),
+                        d->detachCapacity(size() + (last - first)),
                         d->detachFlags() | Data::Grow));
 
             detached.d->copyAppend(first, last);
@@ -205,7 +205,7 @@ public:
         if (d->ref.isShared()
                 || capacity() - size() < size_t(last - first)) {
             SimpleVector detached(Data::allocate(
-                        qMax(capacity(), size() + (last - first)),
+                        d->detachCapacity(size() + (last - first)),
                         d->detachFlags() | Data::Grow));
 
             if (d->size) {
@@ -245,7 +245,7 @@ public:
         if (d->ref.isShared()
                 || capacity() - size() < size_t(last - first)) {
             SimpleVector detached(Data::allocate(
-                        qMax(capacity(), size() + (last - first)),
+                        d->detachCapacity(size() + (last - first)),
                         d->detachFlags() | Data::Grow));
 
             if (position)
diff --git a/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp b/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp
index 6d3bbf046f..b3b8040b1c 100644
--- a/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp
+++ b/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp
@@ -1175,8 +1175,10 @@ void tst_QArrayData::setSharable_data()
 
     QArrayDataPointer<int> emptyReserved(QTypedArrayData<int>::allocate(5,
                 QArrayData::CapacityReserved));
-    QArrayDataPointer<int> nonEmpty(QTypedArrayData<int>::allocate(10,
+    QArrayDataPointer<int> nonEmpty(QTypedArrayData<int>::allocate(5,
                 QArrayData::Default));
+    QArrayDataPointer<int> nonEmptyExtraCapacity(
+            QTypedArrayData<int>::allocate(10, QArrayData::Default));
     QArrayDataPointer<int> nonEmptyReserved(QTypedArrayData<int>::allocate(15,
                 QArrayData::CapacityReserved));
     QArrayDataPointer<int> staticArray(
@@ -1185,13 +1187,15 @@ void tst_QArrayData::setSharable_data()
             QTypedArrayData<int>::fromRawData(staticArrayData.data, 10));
 
     nonEmpty->copyAppend(5, 1);
+    nonEmptyExtraCapacity->copyAppend(5, 1);
     nonEmptyReserved->copyAppend(7, 2);
 
     QTest::newRow("shared-null") << null << size_t(0) << size_t(0) << false << 0;
     QTest::newRow("shared-empty") << empty << size_t(0) << size_t(0) << false << 0;
     // unsharable-empty implicitly tested in shared-empty
     QTest::newRow("empty-reserved") << emptyReserved << size_t(0) << size_t(5) << true << 0;
-    QTest::newRow("non-empty") << nonEmpty << size_t(5) << size_t(10) << false << 1;
+    QTest::newRow("non-empty") << nonEmpty << size_t(5) << size_t(5) << false << 1;
+    QTest::newRow("non-empty-extra-capacity") << nonEmptyExtraCapacity << size_t(5) << size_t(10) << false << 1;
     QTest::newRow("non-empty-reserved") << nonEmptyReserved << size_t(7) << size_t(15) << true << 2;
     QTest::newRow("static-array") << staticArray << size_t(10) << size_t(0) << false << 3;
     QTest::newRow("raw-data") << rawData << size_t(10) << size_t(0) << false << 3;
@@ -1229,8 +1233,10 @@ void tst_QArrayData::setSharable()
     // Unshare, must detach
     array.setSharable(false);
 
-    // Immutability (alloc == 0) is lost on detach
-    if (capacity == 0 && size != 0)
+    // Immutability (alloc == 0) is lost on detach, as is additional capacity
+    // if capacityReserved flag is not set.
+    if ((capacity == 0 && size != 0)
+            || (!isCapacityReserved && capacity > size))
         capacity = size;
 
     QVERIFY(!array->ref.isShared());