diff --git a/Source/Core/Rendering/TextLabel.cs b/Source/Core/Rendering/TextLabel.cs
index 125ae7f0..0fd59691 100755
--- a/Source/Core/Rendering/TextLabel.cs
+++ b/Source/Core/Rendering/TextLabel.cs
@@ -467,6 +467,21 @@ namespace CodeImp.DoomBuilder.Rendering
 
 		// This (re)loads the resources
 		public void ReloadResource() { }
+
+		/// <summary>
+		/// Checks if the whole label is in the viewport.
+		/// </summary>
+		/// <returns>true if the label in in the viewport, false if it isn't</returns>
+		public bool IsInViewport()
+		{
+			(double width, double height) = texturesize.IsEmpty ? ( 0, 0 ) : (texturesize.Width, texturesize.Height);
+
+			return
+				location.x >= (General.Map.CRenderer2D.Viewport.X - width) &&
+				location.x < (General.Map.CRenderer2D.Viewport.X + General.Map.CRenderer2D.Viewport.Width + width) &&
+				location.y <= (General.Map.CRenderer2D.Viewport.Y - height) &&
+				location.y > (General.Map.CRenderer2D.Viewport.Y + General.Map.CRenderer2D.Viewport.Height + height);
+		}
 		
 		#endregion
 	}
diff --git a/Source/Plugins/BuilderModes/ClassicModes/LinedefsMode.cs b/Source/Plugins/BuilderModes/ClassicModes/LinedefsMode.cs
index 84bac16e..86b338e4 100755
--- a/Source/Plugins/BuilderModes/ClassicModes/LinedefsMode.cs
+++ b/Source/Plugins/BuilderModes/ClassicModes/LinedefsMode.cs
@@ -366,8 +366,14 @@ namespace CodeImp.DoomBuilder.BuilderModes
 		//mxd. This sets up new labels
 		private void SetupSectorLabels()
 		{
+			// Dummy label we need for the font
+			TextLabel dummylabel = new TextLabel();
+
+			// The "+" is always shown if the space for the label isn't big enough to show the full text
+			textlabelsizecache["+"] = General.Interface.MeasureString("+", dummylabel.Font).Width;
+
 			// Dispose old labels
-			if(sectorlabels != null)
+			if (sectorlabels != null)
 			{
 				foreach(TextLabel[] larr in sectorlabels.Values)
 					foreach(TextLabel l in larr) l.Dispose();
@@ -396,6 +402,12 @@ namespace CodeImp.DoomBuilder.BuilderModes
 					tagdescarr[1] = "T" + s.Tag;
 				}
 
+				// Add string lengths to the label size cache
+				if (!textlabelsizecache.ContainsKey(tagdescarr[0]))
+					textlabelsizecache[tagdescarr[0]] = General.Interface.MeasureString(tagdescarr[0], dummylabel.Font).Width;
+				if (!textlabelsizecache.ContainsKey(tagdescarr[1]))
+					textlabelsizecache[tagdescarr[1]] = General.Interface.MeasureString(tagdescarr[1], dummylabel.Font).Width;
+
 				// Add to collection
 				sectortexts.Add(s, tagdescarr);
 
@@ -501,19 +513,17 @@ namespace CodeImp.DoomBuilder.BuilderModes
 						TextLabel[] labelarray = sectorlabels[group.Key];
 						for (int i = 0; i < group.Key.Labels.Count; i++)
 						{
+							// Only process this label if it's actually in view
+							if (!labelarray[i].IsInViewport())
+								continue;
+
 							TextLabel l = labelarray[i];
 
 							// Render only when enough space for the label to see
-							if (!textlabelsizecache.ContainsKey(group.Value[0]))
-								textlabelsizecache[group.Value[0]] = General.Interface.MeasureString(group.Value[0], l.Font).Width;
-
 							float requiredsize = textlabelsizecache[group.Value[0]] / 2 / renderer.Scale;
 
 							if (requiredsize > group.Key.Labels[i].radius)
 							{
-								if (!textlabelsizecache.ContainsKey(group.Value[1]))
-									textlabelsizecache[group.Value[1]] = General.Interface.MeasureString(group.Value[1], l.Font).Width;
-
 								requiredsize = textlabelsizecache[group.Value[1]] / 2 / renderer.Scale;
 
 								string newtext;