diff --git a/aegisub/src/auto4_lua_progresssink.cpp b/aegisub/src/auto4_lua_progresssink.cpp
index a9b9c48a7..d9b341db1 100644
--- a/aegisub/src/auto4_lua_progresssink.cpp
+++ b/aegisub/src/auto4_lua_progresssink.cpp
@@ -177,7 +177,7 @@ namespace Automation4 {
 		}
 
 		// Top of stack is now a string to output
-		ps->Log(lua_tostring(L, 1));
+		ps->Log(luaL_checkstring(L, 1));
 		return 0;
 	}