diff --git a/autotests/libs/collectionattributetest.h b/autotests/libs/collectionattributetest.h
--- a/autotests/libs/collectionattributetest.h
+++ b/autotests/libs/collectionattributetest.h
@@ -32,6 +32,7 @@
     void testDefaultAttributes();
     void testCollectionRightsAttribute();
     void testCollectionIdentificationAttribute();
+    void testDetach();
 };
 
 #endif
diff --git a/autotests/libs/collectionattributetest.cpp b/autotests/libs/collectionattributetest.cpp
--- a/autotests/libs/collectionattributetest.cpp
+++ b/autotests/libs/collectionattributetest.cpp
@@ -240,3 +240,18 @@
     QCOMPARE(parsed.identifier(), id);
     QCOMPARE(parsed.collectionNamespace(), ns);
 }
+
+void CollectionAttributeTest::testDetach()
+{
+    // GIVEN a collection with an attribute
+    Collection col;
+    col.attribute<TestAttribute>(Akonadi::Collection::AddIfMissing);
+    Collection col2 = col; // and a copy, so that non-const access detaches
+
+    // WHEN
+    TestAttribute *attr = col2.attribute<TestAttribute>(Akonadi::Collection::AddIfMissing);
+    TestAttribute *attr2 = col2.attribute<TestAttribute>();
+
+    // THEN
+    QCOMPARE(attr, attr2);
+}
diff --git a/src/core/collection.h b/src/core/collection.h
--- a/src/core/collection.h
+++ b/src/core/collection.h
@@ -565,10 +565,10 @@
     Q_UNUSED(option);
 
     const QByteArray type = T().type();
+    markAttributeModified(type); // do this first in case it detaches
     if (hasAttribute(type)) {
         T *attr = dynamic_cast<T *>(attribute(type));
         if (attr) {
-            markAttributeModified(type);
             return attr;
         }
         //Reuse 5250
diff --git a/src/core/tag.h b/src/core/tag.h
--- a/src/core/tag.h
+++ b/src/core/tag.h
@@ -217,10 +217,10 @@
     Q_UNUSED(option);
 
     const QByteArray type = T().type();
+    markAttributeModified(type);
     if (hasAttribute(type)) {
         T *attr = dynamic_cast<T *>(attribute(type));
         if (checkAttribute(attr, type)) {
-            markAttributeModified(type);
             return attr;
         }
     }