diff --git a/src/FSharpLint.Core/Rules/Conventions/SourceLength/SourceLengthHelper.fs b/src/FSharpLint.Core/Rules/Conventions/SourceLength/SourceLengthHelper.fs
index 0099d4995..0eae2947d 100644
--- a/src/FSharpLint.Core/Rules/Conventions/SourceLength/SourceLengthHelper.fs
+++ b/src/FSharpLint.Core/Rules/Conventions/SourceLength/SourceLengthHelper.fs
@@ -69,7 +69,7 @@ let checkSourceLengthRule (config:Config) range fileContents errorName (skipRang
         let sourceCodeLines = sourceCode.Split([| '\n'; '\r' |]) 
         let blankLinesCount = 
             sourceCodeLines
-            |> Seq.filter (fun line -> line.Trim().Length = 0)
+            |> Seq.filter (fun line -> line.AsSpan().IsWhiteSpace())
             |> Seq.length
 
         let skippedLinesCount =