diff --git a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day10.fs b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day10.fs
index 9e3115b..637373e 100644
--- a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day10.fs
+++ b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day10.fs
@@ -88,7 +88,7 @@ module Day10 =
         let mutable pointB =
             let pos = ofRowAndCol lineLength (startLine - 1) startCol
 
-            match s.[pos] with
+            match if pos >= 0 then s.[pos] else 'n' with
             | '|'
             | '7'
             | 'F' -> pos
@@ -96,7 +96,7 @@ module Day10 =
 
             let pos = ofRowAndCol lineLength (startLine + 1) startCol
 
-            match s.[pos] with
+            match if pos < s.Length then s.[pos] else 'n' with
             | '|'
             | 'L'
             | 'J' -> pos
@@ -104,7 +104,7 @@ module Day10 =
 
             let pos = ofRowAndCol lineLength startLine (startCol + 1)
 
-            match s.[pos] with
+            match if pos < s.Length then s.[pos] else 'n' with
             | '-'
             | 'J'
             | '7' -> pos