4 files changed, 23 insertions, 1 deletions
diff --git a/src/gui/text/qfragmentmap_p.h b/src/gui/text/qfragmentmap_p.h
index 501bfff..4057142 100644
--- a/src/gui/text/qfragmentmap_p.h
+++ b/src/gui/text/qfragmentmap_p.h
@@ -195,6 +195,10 @@ public:
         head->root = new_root;
     }
 
+    inline bool isValid(uint n) const {
+        return n > 0 && n != head->freelist;
+    }
+
     union {
         Header *head;
         Fragment *fragments;
@@ -854,6 +858,7 @@ public:
         return data.fragment(index);
     }
     inline uint position(uint node, uint field = 0) const { return data.position(node, field); }
+    inline bool isValid(uint n) const { return data.isValid(n); }
     inline uint next(uint n) const { return data.next(n); }
     inline uint previous(uint n) const { return data.previous(n); }
     inline uint size(uint node, uint field = 0) const { return data.size(node, field); }
diff --git a/src/gui/text/qtextobject.cpp b/src/gui/text/qtextobject.cpp
index 0a9dff8..5c1c8b9 100644
--- a/src/gui/text/qtextobject.cpp
+++ b/src/gui/text/qtextobject.cpp
@@ -891,6 +891,11 @@ QTextBlockUserData::~QTextBlockUserData()
     Returns true if this text block is valid; otherwise returns false.
 */
 
+bool QTextBlock::isValid() const
+{
+    return p != 0 && p->blockMap().isValid(n);
+}
+
 /*!
     \fn QTextBlock &QTextBlock::operator=(const QTextBlock &other)
 
diff --git a/src/gui/text/qtextobject.h b/src/gui/text/qtextobject.h
index 2e588c2..ad8e657 100644
--- a/src/gui/text/qtextobject.h
+++ b/src/gui/text/qtextobject.h
@@ -205,7 +205,7 @@ public:
     inline QTextBlock(const QTextBlock &o) : p(o.p), n(o.n) {}
     inline QTextBlock &operator=(const QTextBlock &o) { p = o.p; n = o.n; return *this; }
 
-    inline bool isValid() const { return p != 0 && n != 0; }
+    bool isValid() const;
 
     inline bool operator==(const QTextBlock &o) const { return p == o.p && n == o.n; }
     inline bool operator!=(const QTextBlock &o) const { return p != o.p || n != o.n; }
diff --git a/tests/auto/qtextblock/tst_qtextblock.cpp b/tests/auto/qtextblock/tst_qtextblock.cpp
index cec3a6a..748d921 100644
--- a/tests/auto/qtextblock/tst_qtextblock.cpp
+++ b/tests/auto/qtextblock/tst_qtextblock.cpp
@@ -76,6 +76,7 @@ private slots:
     void excludeParagraphSeparatorFragment();
     void backwardsBlockIterator();
     void previousBlock_qtbug18026();
+    void removedBlock_qtbug18500();
 
 private:
     QTextDocument *doc;
@@ -181,5 +182,16 @@ void tst_QTextBlock::previousBlock_qtbug18026()
     QVERIFY(last.isValid());
 }
 
+void tst_QTextBlock::removedBlock_qtbug18500()
+{
+    cursor.insertText("line 1\nline 2\nline 3 \nline 4\n");
+    cursor.setPosition(7);
+    QTextBlock block = cursor.block();
+    cursor.setPosition(21, QTextCursor::KeepAnchor);
+
+    cursor.removeSelectedText();
+    QVERIFY(!block.isValid());
+}
+
 QTEST_MAIN(tst_QTextBlock)
 #include "tst_qtextblock.moc"