diff --git a/SqlDatabaseVectorSearch/TextChunkers/Implementations/PlainTextChunker.cs b/SqlDatabaseVectorSearch/TextChunkers/Implementations/PlainTextChunker.cs
index be81fd9..80c25e0 100644
--- a/SqlDatabaseVectorSearch/TextChunkers/Implementations/PlainTextChunker.cs
+++ b/SqlDatabaseVectorSearch/TextChunkers/Implementations/PlainTextChunker.cs
@@ -44,7 +44,6 @@ internal static class PlainTextChunker
     /// <returns>The number of tokens in the input string.</returns>
     public delegate int TokenCounter(string input);
 
-    private static readonly char[] spaceChar = [' '];
     private static readonly string?[] plainTextSplitOptions = ["\n", ".。．", "?!", ";", ":", ",，、", ")]}", " ", "-", null];
     private static readonly string?[] markdownSplitOptions = [".\u3002\uFF0E", "?!", ";", ":", ",\uFF0C\u3001", ")]}", " ", "-", "\n\r", null];
 
@@ -55,8 +54,13 @@ internal static class PlainTextChunker
     /// <param name="maxTokensPerLine">Maximum number of tokens per line.</param>
     /// <param name="tokenCounter">Function to count tokens in a string. If not supplied, the default counter will be used.</param>
     /// <returns>List of lines.</returns>
-    public static List<string> SplitPlainTextLines(string text, int maxTokensPerLine, TokenCounter? tokenCounter = null) =>
-        InternalSplitLines(text, maxTokensPerLine, trim: true, plainTextSplitOptions, tokenCounter);
+    public static List<string> SplitPlainTextLines(string text, int maxTokensPerLine, TokenCounter? tokenCounter = null)
+    {
+        ArgumentNullException.ThrowIfNull(text);
+        ValidateMaxTokens(maxTokensPerLine, nameof(maxTokensPerLine));
+
+        return InternalSplitLines(text, maxTokensPerLine, trim: true, plainTextSplitOptions, tokenCounter);
+    }
 
     /// <summary>
     /// Split markdown text into lines.
@@ -65,8 +69,13 @@ internal static class PlainTextChunker
     /// <param name="maxTokensPerLine">Maximum number of tokens per line.</param>
     /// <param name="tokenCounter">Function to count tokens in a string. If not supplied, the default counter will be used.</param>
     /// <returns>List of lines.</returns>
-    public static List<string> SplitMarkDownLines(string text, int maxTokensPerLine, TokenCounter? tokenCounter = null) =>
-        InternalSplitLines(text, maxTokensPerLine, trim: true, markdownSplitOptions, tokenCounter);
+    public static List<string> SplitMarkdownLines(string text, int maxTokensPerLine, TokenCounter? tokenCounter = null)
+    {
+        ArgumentNullException.ThrowIfNull(text);
+        ValidateMaxTokens(maxTokensPerLine, nameof(maxTokensPerLine));
+
+        return InternalSplitLines(text, maxTokensPerLine, trim: true, markdownSplitOptions, tokenCounter);
+    }
 
     /// <summary>
     /// Split plain text into paragraphs.
@@ -78,7 +87,7 @@ internal static class PlainTextChunker
     /// <param name="tokenCounter">Function to count tokens in a string. If not supplied, the default counter will be used.</param>
     /// <returns>List of paragraphs.</returns>
     public static List<string> SplitPlainTextParagraphs(IEnumerable<string> lines, int maxTokensPerParagraph, int overlapTokens = 0, string? chunkHeader = null, TokenCounter? tokenCounter = null)
-        => InternalSplitTextParagraphs(lines.Select(line => line.Replace("\r\n", "\n").Replace('\r', '\n')), maxTokensPerParagraph, overlapTokens, chunkHeader,
+        => InternalSplitTextParagraphs(lines, maxTokensPerParagraph, overlapTokens, chunkHeader,
             static (text, maxTokens, tokenCounter) => InternalSplitLines(text, maxTokens, trim: false, plainTextSplitOptions, tokenCounter), tokenCounter);
 
     /// <summary>
@@ -96,17 +105,20 @@ internal static class PlainTextChunker
 
     private static List<string> InternalSplitTextParagraphs(IEnumerable<string> lines, int maxTokensPerParagraph, int overlapTokens, string? chunkHeader, Func<string, int, TokenCounter?, List<string>> longLinesSplitter, TokenCounter? tokenCounter)
     {
-        if (maxTokensPerParagraph <= 0)
+        ArgumentNullException.ThrowIfNull(lines);
+        ValidateMaxTokens(maxTokensPerParagraph, nameof(maxTokensPerParagraph));
+
+        if (overlapTokens < 0)
         {
-            throw new ArgumentException("maxTokensPerParagraph should be a positive number", nameof(maxTokensPerParagraph));
+            throw new ArgumentOutOfRangeException(nameof(overlapTokens), "overlapTokens cannot be negative.");
         }
 
         if (maxTokensPerParagraph <= overlapTokens)
         {
-            throw new ArgumentException("overlapTokens cannot be larger than maxTokensPerParagraph", nameof(maxTokensPerParagraph));
+            throw new ArgumentException("overlapTokens cannot be larger than or equal to maxTokensPerParagraph.", nameof(overlapTokens));
         }
 
-        // Optimize empty inputs if we can efficiently determine the're empty
+        // Optimize empty inputs if we can efficiently determine they're empty.
         if (lines is ICollection<string> c && c.Count == 0)
         {
             return [];
@@ -114,9 +126,13 @@ internal static class PlainTextChunker
 
         var chunkHeaderTokens = chunkHeader is { Length: > 0 } ? GetTokenCount(chunkHeader, tokenCounter) : 0;
         var adjustedMaxTokensPerParagraph = maxTokensPerParagraph - overlapTokens - chunkHeaderTokens;
+        if (adjustedMaxTokensPerParagraph <= 0)
+        {
+            throw new ArgumentException("chunkHeader and overlapTokens must leave room for paragraph content.", nameof(chunkHeader));
+        }
 
         // Split long lines first
-        var truncatedLines = lines.SelectMany(line => longLinesSplitter(line, adjustedMaxTokensPerParagraph, tokenCounter));
+        var truncatedLines = lines.SelectMany(line => longLinesSplitter(NormalizeLineEndings(line), adjustedMaxTokensPerParagraph, tokenCounter));
 
         var paragraphs = BuildParagraph(truncatedLines, adjustedMaxTokensPerParagraph, tokenCounter);
         var processedParagraphs = ProcessParagraphs(paragraphs, adjustedMaxTokensPerParagraph, overlapTokens, chunkHeader, longLinesSplitter, tokenCounter);
@@ -174,18 +190,11 @@ internal static class PlainTextChunker
 
             if (GetTokenCount(lastParagraph, tokenCounter) < adjustedMaxTokensPerParagraph / 4)
             {
-                var lastParagraphTokens = lastParagraph.Split(spaceChar, StringSplitOptions.RemoveEmptyEntries);
-                var secondLastParagraphTokens = secondLastParagraph.Split(spaceChar, StringSplitOptions.RemoveEmptyEntries);
+                var mergedParagraph = $"{secondLastParagraph} {lastParagraph}";
 
-                var lastParagraphTokensCount = lastParagraphTokens.Length;
-                var secondLastParagraphTokensCount = secondLastParagraphTokens.Length;
-
-                if (lastParagraphTokensCount + secondLastParagraphTokensCount <= adjustedMaxTokensPerParagraph)
+                if (GetTokenCount(mergedParagraph, tokenCounter) <= adjustedMaxTokensPerParagraph)
                 {
-                    var newSecondLastParagraph = string.Join(" ", secondLastParagraphTokens);
-                    var newLastParagraph = string.Join(" ", lastParagraphTokens);
-
-                    paragraphs[^2] = $"{newSecondLastParagraph} {newLastParagraph}";
+                    paragraphs[^2] = mergedParagraph;
                     paragraphs.RemoveAt(paragraphs.Count - 1);
                 }
             }
@@ -232,7 +241,7 @@ internal static class PlainTextChunker
     {
         var result = new StringListWithTokenCount(tokenCounter);
 
-        text = text.Replace("\r\n", "\n"); // normalize line endings
+        text = NormalizeLineEndings(text);
         result.Add(text);
         for (var i = 0; i < splitOptions.Length; i++)
         {
@@ -314,9 +323,9 @@ internal static class PlainTextChunker
                 }
 
                 // Recursion
-                var (splits1, split1) = Split(firstHalf, null, maxTokens, separators, trim, tokenCounter, GetTokenCount(firstHalf.ToString(), tokenCounter));
+                var (splits1, split1) = Split(firstHalf, null, maxTokens, separators, trim, tokenCounter, GetTokenCount(firstHalf, tokenCounter));
                 result.AddRange(splits1);
-                var (splits2, split2) = Split(secondHalf, null, maxTokens, separators, trim, tokenCounter, GetTokenCount(secondHalf.ToString(), tokenCounter));
+                var (splits2, split2) = Split(secondHalf, null, maxTokens, separators, trim, tokenCounter, GetTokenCount(secondHalf, tokenCounter));
                 result.AddRange(splits2);
 
                 inputWasSplit = split1 || split2;
@@ -326,10 +335,14 @@ internal static class PlainTextChunker
 
         var resultString = inputString ?? input.ToString();
         var resultTokenCount = inputTokenCount;
-        if (trim && !resultString.Trim().Equals(resultString, StringComparison.Ordinal))
+        if (trim)
         {
-            resultString = resultString.Trim();
-            resultTokenCount = GetTokenCount(resultString, tokenCounter);
+            var trimmedResult = resultString.Trim();
+            if (!trimmedResult.Equals(resultString, StringComparison.Ordinal))
+            {
+                resultString = trimmedResult;
+                resultTokenCount = GetTokenCount(resultString, tokenCounter);
+            }
         }
 
         result.Add(resultString, resultTokenCount);
@@ -339,9 +352,21 @@ internal static class PlainTextChunker
 
     private static int GetTokenCount(string input, TokenCounter? tokenCounter) => tokenCounter is null ? GetDefaultTokenCount(input.Length) : tokenCounter(input);
 
+    private static int GetTokenCount(ReadOnlySpan<char> input, TokenCounter? tokenCounter) => tokenCounter is null ? GetDefaultTokenCount(input.Length) : tokenCounter(input.ToString());
+
+    private static string NormalizeLineEndings(string text) => text.Replace("\r\n", "\n").Replace('\r', '\n');
+
+    private static void ValidateMaxTokens(int maxTokens, string parameterName)
+    {
+        if (maxTokens <= 0)
+        {
+            throw new ArgumentOutOfRangeException(parameterName, "The maximum token count must be a positive number.");
+        }
+    }
+
     private static int GetDefaultTokenCount(int length)
     {
         Debug.Assert(length >= 0);
-        return length >> 2;
+        return length == 0 ? 0 : Math.Max(1, length >> 2);
     }
 }
\ No newline at end of file
diff --git a/SqlDatabaseVectorSearch/TextChunkers/MarkdownTextChunker.cs b/SqlDatabaseVectorSearch/TextChunkers/MarkdownTextChunker.cs
index 37a06e7..ebea231 100644
--- a/SqlDatabaseVectorSearch/TextChunkers/MarkdownTextChunker.cs
+++ b/SqlDatabaseVectorSearch/TextChunkers/MarkdownTextChunker.cs
@@ -11,7 +11,7 @@ public class MarkdownTextChunker(TokenizerService tokenizerService, IOptions<App
 
     public IList<string> Split(string text)
     {
-        var lines = PlainTextChunker.SplitMarkDownLines(text, appSettings.MaxTokensPerLine, tokenizerService.CountEmbeddingTokens);
+        var lines = PlainTextChunker.SplitMarkdownLines(text, appSettings.MaxTokensPerLine, tokenizerService.CountEmbeddingTokens);
         var paragraphs = PlainTextChunker.SplitMarkdownParagraphs(lines, appSettings.MaxTokensPerParagraph, appSettings.OverlapTokens, tokenCounter: tokenizerService.CountEmbeddingTokens);
 
         return paragraphs;