diff --git a/library/include/modules/Units.h b/library/include/modules/Units.h
index c719a60a9..e2d34254d 100644
--- a/library/include/modules/Units.h
+++ b/library/include/modules/Units.h
@@ -181,9 +181,9 @@ DFHACK_EXPORT std::string getCasteProfessionName(int race, int caste, df::profes
 DFHACK_EXPORT int8_t getProfessionColor(df::unit *unit, bool ignore_noble = false);
 DFHACK_EXPORT int8_t getCasteProfessionColor(int race, int caste, df::profession pid);
 
-DFHACK_EXPORT df::goal_type getGoalType(df::unit *unit, int goalIndex = 0);
-DFHACK_EXPORT std::string getGoalName(df::unit *unit, int goalIndex = 0);
-DFHACK_EXPORT bool isGoalAchieved(df::unit *unit, int goalIndex = 0);
+DFHACK_EXPORT df::goal_type getGoalType(df::unit *unit, size_t goalIndex = 0);
+DFHACK_EXPORT std::string getGoalName(df::unit *unit, size_t goalIndex = 0);
+DFHACK_EXPORT bool isGoalAchieved(df::unit *unit, size_t goalIndex = 0);
 
 DFHACK_EXPORT std::string getSquadName(df::unit *unit);
 
diff --git a/library/modules/Units.cpp b/library/modules/Units.cpp
index d5c871f5b..a8f96b29f 100644
--- a/library/modules/Units.cpp
+++ b/library/modules/Units.cpp
@@ -1439,7 +1439,7 @@ int8_t Units::getCasteProfessionColor(int race, int casteid, df::profession pid)
     return 3;
 }
 
-df::goal_type Units::getGoalType(df::unit *unit, int goalIndex)
+df::goal_type Units::getGoalType(df::unit *unit, size_t goalIndex)
 {
     CHECK_NULL_POINTER(unit);
 
@@ -1452,7 +1452,7 @@ df::goal_type Units::getGoalType(df::unit *unit, int goalIndex)
     return goal;
 }
 
-std::string Units::getGoalName(df::unit *unit, int goalIndex)
+std::string Units::getGoalName(df::unit *unit, size_t goalIndex)
 {
     CHECK_NULL_POINTER(unit);
 
@@ -1471,7 +1471,7 @@ std::string Units::getGoalName(df::unit *unit, int goalIndex)
     return goal_name;
 }
 
-bool Units::isGoalAchieved(df::unit *unit, int goalIndex)
+bool Units::isGoalAchieved(df::unit *unit, size_t goalIndex)
 {
     CHECK_NULL_POINTER(unit);