diff --git a/modules/seq/base/src/alignment_handle.cc b/modules/seq/base/src/alignment_handle.cc
index cc0f06788eee7c9303581ab25cf291257ec5673f..48bb07af5fb0dad628d188aa32ccbeb722e99fc4 100644
--- a/modules/seq/base/src/alignment_handle.cc
+++ b/modules/seq/base/src/alignment_handle.cc
@@ -226,7 +226,7 @@ AlignedColumnIterator AlignmentHandle::end() const
   return AlignedColumnIterator(*this, this->GetLength(), this->GetLength());
 }
 
-AlignedColumn AlignmentHandle::operator[](int index)
+AlignedColumn AlignmentHandle::operator[](int index) const
 {
   return AlignedColumn(*this, index);
 }
diff --git a/modules/seq/base/src/alignment_handle.hh b/modules/seq/base/src/alignment_handle.hh
index 8523fb1d48bbfdef522ff77973f81bddc4ad7991..7e6ba856767795ae3ef7882f898b7cfffb0559e2 100644
--- a/modules/seq/base/src/alignment_handle.hh
+++ b/modules/seq/base/src/alignment_handle.hh
@@ -135,7 +135,7 @@ public:
   /// This method does not throw any exception. Upon accessing methods of the 
   /// aligned column, exceptions might be thrown when the index is out of 
   /// bounds.
-  AlignedColumn operator[](int index);
+  AlignedColumn operator[](int index) const;
   
   AlignmentHandle(const impl::SequenceListImplPtr& impl);