diff --git a/src/ai/api/ai_sign.cpp b/src/ai/api/ai_sign.cpp
index dd164c6ca2..29609f29ab 100644
--- a/src/ai/api/ai_sign.cpp
+++ b/src/ai/api/ai_sign.cpp
@@ -15,7 +15,7 @@
 
 /* static */ SignID AISign::GetMaxSignID()
 {
-	return (SignID)::Sign::GetNumItems();
+	return (SignID)::Sign::GetPoolSize();
 }
 
 /* static */ bool AISign::IsValidSign(SignID sign_id)