diff --git a/CHANGELOG.md b/CHANGELOG.md
index b4cfca745..c80c15f69 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 ## Changelog
 
+0.7.3:
+
+- @PhantomGamers: Fixed error when upgrading blueprint previews.
+- @sp00ktober: Added hotfix to prevent error caused by ILS ships
+
 0.7.2:
 
 - @sp00ktober: Fixed issue where the host would render buildings placed by players on other planets on his current planet.
diff --git a/NebulaModel/Packets/Factory/UpgradeEntityRequest.cs b/NebulaModel/Packets/Factory/UpgradeEntityRequest.cs
index c420497ae..94f9759a1 100644
--- a/NebulaModel/Packets/Factory/UpgradeEntityRequest.cs
+++ b/NebulaModel/Packets/Factory/UpgradeEntityRequest.cs
@@ -8,15 +8,17 @@ public class UpgradeEntityRequest
         public Float3 pos { get; set; }
         public Float4 rot { get; set; }
         public int UpgradeProtoId { get; set; }
+        public bool IsPrebuild { get; set; }
         public int AuthorId { get; set; }
 
         public UpgradeEntityRequest() { }
-        public UpgradeEntityRequest(int planetId, Float3 pos, Float4 rot, int upgradeProtoId, int authorId)
+        public UpgradeEntityRequest(int planetId, Float3 pos, Float4 rot, int upgradeProtoId, bool isPrebuild, int authorId)
         {
             PlanetId = planetId;
             this.pos = pos;
             this.rot = rot;
             UpgradeProtoId = upgradeProtoId;
+            IsPrebuild = isPrebuild;
             AuthorId = authorId;
         }
     }
diff --git a/NebulaNetwork/PacketProcessors/Factory/Entity/UpgradeEntityRequestProcessor.cs b/NebulaNetwork/PacketProcessors/Factory/Entity/UpgradeEntityRequestProcessor.cs
index 3479645ac..08c85de8f 100644
--- a/NebulaNetwork/PacketProcessors/Factory/Entity/UpgradeEntityRequestProcessor.cs
+++ b/NebulaNetwork/PacketProcessors/Factory/Entity/UpgradeEntityRequestProcessor.cs
@@ -31,20 +31,29 @@ public override void ProcessPacket(UpgradeEntityRequest packet, NebulaConnection
 
                 Quaternion qRot = new Quaternion(packet.rot.x, packet.rot.y, packet.rot.z, packet.rot.w);
                 Vector3 vPos = new Vector3(packet.pos.x, packet.pos.y, packet.pos.z);
-                EntityData[] ePool = planet.factory.entityPool;
 
-                for (int i = 1; i < planet.factory.entityCursor; i++)
+                if (packet.IsPrebuild)
                 {
-                    if(ePool[i].pos == vPos && ePool[i].rot == qRot)
+                    for (int i = 1; i < planet.factory.prebuildCursor; i++)
                     {
-                        // setting specifyPlanet here to avoid accessing a null object (see GPUInstancingManager activePlanet getter)
-                        PlanetData pData = GameMain.gpuiManager.specifyPlanet;
-
-                        GameMain.gpuiManager.specifyPlanet = GameMain.galaxy.PlanetById(packet.PlanetId);
-                        planet.factory.UpgradeFinally(GameMain.mainPlayer, i, itemProto);
-                        GameMain.gpuiManager.specifyPlanet = pData;
-
-                        break;
+                        PrebuildData pbData = planet.factory.prebuildPool[i];
+                        if (pbData.pos == vPos && pbData.rot == qRot)
+                        {
+                            DoUpgrade(planet, -i, itemProto);
+                            break;
+                        }
+                    }
+                }
+                else
+                {
+                    for (int i = 1; i < planet.factory.entityCursor; i++)
+                    {
+                        EntityData eData = planet.factory.entityPool[i];
+                        if (eData.pos == vPos && eData.rot == qRot)
+                        {
+                            DoUpgrade(planet, i, itemProto);
+                            break;
+                        }
                     }
                 }
 
@@ -52,5 +61,15 @@ public override void ProcessPacket(UpgradeEntityRequest packet, NebulaConnection
                 Multiplayer.Session.Factories.PacketAuthor = NebulaModAPI.AUTHOR_NONE;
             }
         }
+
+        private static void DoUpgrade(PlanetData planet, int objId, ItemProto itemProto)
+        {
+            // setting specifyPlanet here to avoid accessing a null object (see GPUInstancingManager activePlanet getter)
+            PlanetData pData = GameMain.gpuiManager.specifyPlanet;
+
+            GameMain.gpuiManager.specifyPlanet = planet;
+            planet.factory.UpgradeFinally(GameMain.mainPlayer, objId, itemProto);
+            GameMain.gpuiManager.specifyPlanet = pData;
+        }
     }
 }
diff --git a/NebulaPatcher/Patches/Dynamic/PlanetFactory_Patch.cs b/NebulaPatcher/Patches/Dynamic/PlanetFactory_Patch.cs
index c9fcab0fa..09600edd5 100644
--- a/NebulaPatcher/Patches/Dynamic/PlanetFactory_Patch.cs
+++ b/NebulaPatcher/Patches/Dynamic/PlanetFactory_Patch.cs
@@ -72,11 +72,34 @@ public static bool UpgradeFinally_Prefix(PlanetFactory __instance, Player player
                 return true;
             }
 
+            if (objId == 0 || replace_item_proto == null)
+            {
+                return false;
+            }
+
             if (Multiplayer.Session.LocalPlayer.IsHost || !Multiplayer.Session.Factories.IsIncomingRequest.Value)
             {
-                EntityData eData = __instance.entityPool[objId];
+                bool isPrebuild = false;
+                Vector3 pos;
+                Quaternion rot;
+
+                if (objId > 0)
+                {
+                    // real entity
+                    EntityData eData = __instance.entityPool[objId];
+                    pos = eData.pos;
+                    rot = eData.rot;
+                }
+                else
+                {
+                    // blueprint build preview
+                    PrebuildData pData = __instance.prebuildPool[-objId];
+                    pos = pData.pos;
+                    rot = pData.rot;
+                    isPrebuild = true;
+                }
 
-                Multiplayer.Session.Network.SendPacket(new UpgradeEntityRequest(__instance.planetId, new Float3(eData.pos.x, eData.pos.y, eData.pos.z), new Float4(eData.rot.x, eData.rot.y, eData.rot.z, eData.rot.w), replace_item_proto.ID, Multiplayer.Session.Factories.PacketAuthor == -1 ? Multiplayer.Session.LocalPlayer.Id : Multiplayer.Session.Factories.PacketAuthor));
+                Multiplayer.Session.Network.SendPacket(new UpgradeEntityRequest(__instance.planetId, new Float3(pos.x, pos.y, pos.z), new Float4(rot.x, rot.y, rot.z, rot.w), replace_item_proto.ID, isPrebuild, Multiplayer.Session.Factories.PacketAuthor == -1 ? Multiplayer.Session.LocalPlayer.Id : Multiplayer.Session.Factories.PacketAuthor));
             }
 
             return Multiplayer.Session.LocalPlayer.IsHost || Multiplayer.Session.Factories.IsIncomingRequest.Value;
diff --git a/version.json b/version.json
index 6fd1f442e..4d84aa200 100644
--- a/version.json
+++ b/version.json
@@ -1,6 +1,6 @@
 {
   "$schema": "https://raw.githubusercontent.com/dotnet/Nerdbank.GitVersioning/master/src/NerdBank.GitVersioning/version.schema.json",
-  "version": "0.7.2",
+  "version": "0.7.3",
   "assemblyVersion": {
     "precision": "build"
   },