diff --git a/libhdt/src/triples/BitmapTriplesIterators.cpp b/libhdt/src/triples/BitmapTriplesIterators.cpp
index e975966a..88fa4ffa 100644
--- a/libhdt/src/triples/BitmapTriplesIterators.cpp
+++ b/libhdt/src/triples/BitmapTriplesIterators.cpp
@@ -785,7 +785,7 @@ void ObjectIndexIterator::updateOutput() {
 
 bool ObjectIndexIterator::hasNext()
 {
-    return posIndex <= maxIndex;
+    return posIndex <= maxIndex && maxIndex >= 0;
 }
 
 TripleID *ObjectIndexIterator::next()