diff --git a/Source/Core/Map/BSP.cs b/Source/Core/Map/BSP.cs
index af1c741..5539142 100644
--- a/Source/Core/Map/BSP.cs
+++ b/Source/Core/Map/BSP.cs
@@ -216,7 +216,7 @@ namespace CodeImp.DoomBuilder.Map
 			for(int i = 0; i < ssectors.Length; i++)
 			{
 				ssectors[i].numsegs = ssecreader.ReadInt16();
-				ssectors[i].firstseg = ssecreader.ReadInt16();
+				ssectors[i].firstseg = ssecreader.ReadUInt16();
 			}
 			ssecreader.Close();
 			ssecstream.Close();
diff --git a/Source/Plugins/NodesViewer/NodesViewerMode.cs b/Source/Plugins/NodesViewer/NodesViewerMode.cs
index 6db6686..3d798f2 100644
--- a/Source/Plugins/NodesViewer/NodesViewerMode.cs
+++ b/Source/Plugins/NodesViewer/NodesViewerMode.cs
@@ -220,7 +220,7 @@ namespace CodeImp.DoomBuilder.Plugins.NodesViewer
 			for(int i = 0; i < ssectors.Length; i++)
 			{
 				ssectors[i].numsegs = ssecreader.ReadInt16();
-				ssectors[i].firstseg = ssecreader.ReadInt16();
+				ssectors[i].firstseg = ssecreader.ReadUInt16();
 			}
 			ssecreader.Close();
 			ssecstream.Close();