diff --git a/src/PdfSharp/Drawing/FontHelper.cs b/src/PdfSharp/Drawing/FontHelper.cs
index bfd35c92..333670b3 100644
--- a/src/PdfSharp/Drawing/FontHelper.cs
+++ b/src/PdfSharp/Drawing/FontHelper.cs
@@ -75,18 +75,48 @@ public static XSize MeasureString(string text, XFont font, XStringFormat stringF
             if (descriptor != null)
             {
                 // Height is the sum of ascender and descender.
-                size.Height = (descriptor.Ascender + descriptor.Descender) * font.Size / font.UnitsPerEm;
+                var singleLineHeight = (descriptor.Ascender + descriptor.Descender) * font.Size / font.UnitsPerEm;
+                var lineGapHeight = (descriptor.LineSpacing - descriptor.Ascender - descriptor.Descender) * font.Size / font.UnitsPerEm;
+
                 Debug.Assert(descriptor.Ascender > 0);
 
                 bool symbol = descriptor.FontFace.cmap.symbol;
                 int length = text.Length;
+                int adjustedLength = length;
+                var height = singleLineHeight;
+                int maxWidth = 0;
                 int width = 0;
                 for (int idx = 0; idx < length; idx++)
                 {
                     char ch = text[idx];
+
+                    // Handle line feed (\n)
+                    if (ch == 10)
+                    {
+                        adjustedLength--;
+                        if (idx < (length - 1))
+                        {
+                            maxWidth = Math.Max(maxWidth, width);
+                            width = 0;
+                            height += lineGapHeight + singleLineHeight;
+                        }
+
+                        continue;
+                    }
+
+                    // HACK: Handle tabulator sign as space (\t)
+                    if (ch == 9)
+                    {
+                        ch = ' ';
+                    }
+
                     // HACK: Unclear what to do here.
                     if (ch < 32)
+                    {
+                        adjustedLength--;
+
                         continue;
+                    }
 
                     if (symbol)
                     {
@@ -97,15 +127,18 @@ public static XSize MeasureString(string text, XFont font, XStringFormat stringF
                     int glyphIndex = descriptor.CharCodeToGlyphIndex(ch);
                     width += descriptor.GlyphIndexToWidth(glyphIndex);
                 }
-                // What? size.Width = width * font.Size * (font.Italic ? 1 : 1) / descriptor.UnitsPerEm;
-                size.Width = width * font.Size / descriptor.UnitsPerEm;
+                maxWidth = Math.Max(maxWidth, width);
+
+                // What? size.Width = maxWidth * font.Size * (font.Italic ? 1 : 1) / descriptor.UnitsPerEm;
+                size.Width = maxWidth * font.Size / descriptor.UnitsPerEm;
+                size.Height = height;
 
                 // Adjust bold simulation.
                 if ((font.GlyphTypeface.StyleSimulations & XStyleSimulations.BoldSimulation) == XStyleSimulations.BoldSimulation)
                 {
                     // Add 2% of the em-size for each character.
                     // Unsure how to deal with white space. Currently count as regular character.
-                    size.Width += length * font.Size * Const.BoldEmphasis;
+                    size.Width += adjustedLength * font.Size * Const.BoldEmphasis;
                 }
             }
             Debug.Assert(descriptor != null, "No OpenTypeDescriptor.");
diff --git a/src/PdfSharp/Fonts.OpenType/GlyphTypefaceCache.cs b/src/PdfSharp/Fonts.OpenType/GlyphTypefaceCache.cs
index c716d3d4..bdbd5fed 100644
--- a/src/PdfSharp/Fonts.OpenType/GlyphTypefaceCache.cs
+++ b/src/PdfSharp/Fonts.OpenType/GlyphTypefaceCache.cs
@@ -27,12 +27,12 @@
 // DEALINGS IN THE SOFTWARE.
 #endregion
 
+using PdfSharp.Drawing;
+using PdfSharp.Internal;
 using System;
+using System.Collections.Concurrent;
 using System.Diagnostics;
-using System.Collections.Generic;
 using System.Text;
-using PdfSharp.Drawing;
-using PdfSharp.Internal;
 
 namespace PdfSharp.Fonts.OpenType
 {
@@ -43,7 +43,7 @@ internal class GlyphTypefaceCache
     {
         GlyphTypefaceCache()
         {
-            _glyphTypefacesByKey = new Dictionary<string, XGlyphTypeface>();
+            _glyphTypefacesByKey = new ConcurrentDictionary<string, XGlyphTypeface>();
         }
 
         public static bool TryGetGlyphTypeface(string key, out XGlyphTypeface glyphTypeface)
@@ -64,7 +64,7 @@ public static void AddGlyphTypeface(XGlyphTypeface glyphTypeface)
                 Lock.EnterFontFactory();
                 GlyphTypefaceCache cache = Singleton;
                 Debug.Assert(!cache._glyphTypefacesByKey.ContainsKey(glyphTypeface.Key));
-                cache._glyphTypefacesByKey.Add(glyphTypeface.Key, glyphTypeface);
+                cache._glyphTypefacesByKey.TryAdd(glyphTypeface.Key, glyphTypeface);
             }
             finally { Lock.ExitFontFactory(); }
         }
@@ -97,7 +97,7 @@ internal static string GetCacheState()
             StringBuilder state = new StringBuilder();
             state.Append("====================\n");
             state.Append("Glyph typefaces by name\n");
-            Dictionary<string, XGlyphTypeface>.KeyCollection familyKeys = Singleton._glyphTypefacesByKey.Keys;
+            var familyKeys = Singleton._glyphTypefacesByKey.Keys;
             int count = familyKeys.Count;
             string[] keys = new string[count];
             familyKeys.CopyTo(keys, 0);
@@ -111,6 +111,6 @@ internal static string GetCacheState()
         /// <summary>
         /// Maps typeface key to glyph typeface.
         /// </summary>
-        readonly Dictionary<string, XGlyphTypeface> _glyphTypefacesByKey;
+        readonly ConcurrentDictionary<string, XGlyphTypeface> _glyphTypefacesByKey;
     }
 }