diff --git a/common/achievements.cpp b/common/achievements.cpp
index 1ad12348576..09f91f41b9e 100644
--- a/common/achievements.cpp
+++ b/common/achievements.cpp
@@ -234,7 +234,7 @@ int AchievementsManager::getStatInt(String const &id) {
 }
 
 
-String AchievementsManager::getStatRaw(String const &id) {
+const String AchievementsManager::getStatRaw(String const &id) {
 	if (!isReady()) {
 		return "";
 	}
diff --git a/common/achievements.h b/common/achievements.h
index 47eb18b6d91..61dd49aeec8 100644
--- a/common/achievements.h
+++ b/common/achievements.h
@@ -166,7 +166,7 @@ public:
 	 *
 	 * @param[in] id	Internal ID of the achievement.
 	 */
-	String getStatRaw(const String &id);
+	const String getStatRaw(const String &id);
 
 	/**
 	 * Get an average rate statistic (float).