diff --git a/Assets/DanmakU/Core/DanmakuExtensions.cs b/Assets/DanmakU/Core/DanmakuExtensions.cs
index 971c9838..9ef54f56 100644
--- a/Assets/DanmakU/Core/DanmakuExtensions.cs
+++ b/Assets/DanmakU/Core/DanmakuExtensions.cs
@@ -851,7 +851,7 @@ public static T MatchPrefab<T> (this T danmakus, DanmakuPrefab prefab) where T :
 
 		#region Fire Functions 
 
-		public static T Fire<T>(this T danmakus, FireData data, bool useRotation  = true) where T : IEnumerable<Danmaku> {
+		public static T Fire<T>(this T danmakus, FireData data, bool useRotation  = true) where T : class, IEnumerable<Danmaku>{
 			if (danmakus == null)
 				return null;
 			if (data == null)
@@ -884,7 +884,7 @@ public static T Fire<T>(this T danmakus, FireData data, bool useRotation  = true
 			return danmakus;
 		}
 
-		public static T Fire<T>(this T danmakus, FireBuilder builder, bool useRotation  = true) where T : IEnumerable<Danmaku> {
+		public static T Fire<T>(this T danmakus, FireBuilder builder, bool useRotation  = true) where T : class, IEnumerable<Danmaku> {
 			if (danmakus == null)
 				return null;
 			if (builder == null)