diff --git a/include/gnss_utils/gnss_utils.h b/include/gnss_utils/gnss_utils.h
index dd594deb1d0a2fd34b050ac19f3c323fcbd155cd..135347a6c21c56b1e4c147940991b20c57ab4a8d 100644
--- a/include/gnss_utils/gnss_utils.h
+++ b/include/gnss_utils/gnss_utils.h
@@ -38,8 +38,10 @@ typedef std::shared_ptr<const Snapshot>     SnapshotConstPtr;
 
 enum Combination
 {
-    CODE_L1,    // only L1 code
-    CARRIER_L1  // only L1 carrier phase
+    CODE_L1,            ///< only L1 code
+    CARRIER_L1,         ///< only L1 carrier phase
+    CODE_IONO_FREE,     ///< iono-free combination for code
+    CARRIER_IONO_FREE   ///< iono-free combination for carrier phase
 };
 
 }