diff --git a/include/kdev-pg-token-stream.h b/include/kdev-pg-token-stream.h
--- a/include/kdev-pg-token-stream.h
+++ b/include/kdev-pg-token-stream.h
@@ -128,22 +128,25 @@
    */
   inline void rewind(qint64 index)
   {
+    Q_ASSERT(0 <= index && index <= size());
     mIndex = index;
   }
   
   /**
    * Returns the token at the specified position in the stream.
    */
   inline T const &at(qint64 index) const
   {
+    Q_ASSERT(0 <= index && index < size());
     return mTokenBuffer[index];
   }
   
   /**
    * Returns the token at the specified position in the stream.
    */
   inline T &at(qint64 index)
   {
+    Q_ASSERT(0 <= index && index < size());
     return mTokenBuffer[index];
   }
   
@@ -184,6 +187,7 @@
    */
   inline T &curr()
   {
+    Q_ASSERT(mIndex < size());
     return mTokenBuffer[mIndex];
   }