diff --git a/src/algorithms/libs/gnss_circular_deque.h b/src/algorithms/libs/gnss_circular_deque.h
index 442797e1f..fe840d4ba 100644
--- a/src/algorithms/libs/gnss_circular_deque.h
+++ b/src/algorithms/libs/gnss_circular_deque.h
@@ -30,8 +30,8 @@ class Gnss_circular_deque
 public:
     Gnss_circular_deque();                                            //!< Default constructor
     Gnss_circular_deque(unsigned int max_size, unsigned int nchann);  //!< nchann = number of channels; max_size = channel capacity
-    unsigned int size(unsigned int ch);                               //!< Returns the number of available elements in a channel
-    T& at(unsigned int ch, unsigned int pos);                         //!< Returns a reference to an element with bount checking
+    unsigned int size(unsigned int ch) const;                         //!< Returns the number of available elements in a channel
+    T& at(unsigned int ch, unsigned int pos);                         //!< Returns a reference to an element with bound checking
     const T& get(unsigned int ch, unsigned int pos) const;            //!< Returns a const reference to an element without bound checking
     T& front(unsigned int ch);                                        //!< Returns a reference to the first element in the deque
     T& back(unsigned int ch);                                         //!< Returns a reference to the last element in the deque
@@ -61,7 +61,7 @@ Gnss_circular_deque<T>::Gnss_circular_deque(unsigned int max_size, unsigned int
 
 
 template <class T>
-unsigned int Gnss_circular_deque<T>::size(unsigned int ch)
+unsigned int Gnss_circular_deque<T>::size(unsigned int ch) const
 {
     return d_data[ch].size();
 }