diff --git a/src/m_cond.c b/src/m_cond.c
index 8c9223c13..d0a911b25 100644
--- a/src/m_cond.c
+++ b/src/m_cond.c
@@ -1252,7 +1252,7 @@ cupheader_t *M_UnlockableCup(unlockable_t *unlock)
 	return cup;
 }
 
-INT16 M_UnlockableMapNum(unlockable_t *unlock)
+UINT16 M_UnlockableMapNum(unlockable_t *unlock)
 {
 	if (unlock->type != SECRET_MAP)
 	{
diff --git a/src/m_cond.h b/src/m_cond.h
index 7dca580da..7aaf6e23a 100644
--- a/src/m_cond.h
+++ b/src/m_cond.h
@@ -226,7 +226,7 @@ UINT8 M_GotLowEnoughTime(INT32 tictime);
 INT32 M_UnlockableSkinNum(unlockable_t *unlock);
 INT32 M_UnlockableFollowerNum(unlockable_t *unlock);
 cupheader_t *M_UnlockableCup(unlockable_t *unlock);
-INT16 M_UnlockableMapNum(unlockable_t *unlock);
+UINT16 M_UnlockableMapNum(unlockable_t *unlock);
 
 INT32 M_EmblemSkinNum(emblem_t *emblem);