diff --git a/src/core/system_parameters/gps_navigation_message.cc b/src/core/system_parameters/gps_navigation_message.cc
index bdae760dd..2dfcc84fe 100644
--- a/src/core/system_parameters/gps_navigation_message.cc
+++ b/src/core/system_parameters/gps_navigation_message.cc
@@ -558,7 +558,7 @@ bool Gps_Navigation_Message::satellite_validation()
 }
 
 
-bool Gps_Navigation_Message::almanac_validation()
+bool Gps_Navigation_Message::almanac_validation() const
 {
     return flag_almanac_valid && (i_WN_A > 0);
 }
diff --git a/src/core/system_parameters/gps_navigation_message.h b/src/core/system_parameters/gps_navigation_message.h
index 9860778fb..eee9717b2 100644
--- a/src/core/system_parameters/gps_navigation_message.h
+++ b/src/core/system_parameters/gps_navigation_message.h
@@ -139,7 +139,7 @@ public:
     }
 
     bool satellite_validation();
-    bool almanac_validation();
+    bool almanac_validation() const;
 
 private:
     uint64_t read_navigation_unsigned(const std::bitset<GPS_SUBFRAME_BITS>& bits, const std::vector<std::pair<int32_t, int32_t>>& parameter) const;