diff --git a/README.md b/README.md
index d070a9d..d03bbea 100644
--- a/README.md
+++ b/README.md
@@ -259,6 +259,12 @@ public class CustomizedMaskedLogs
     [LogMasked(ShowFirst = 3, ShowLast = 3)]
     public string? ShowFirstAndLastThreeAndDefaultMaskInTheMiddle { get; set; }
 
+    /// <summary>
+    /// 123456789 results in "123456789", no mask applied
+    /// </summary>
+    [LogMasked(ShowFirst = -1, ShowLast = -1)]
+    public string? ShowFirstAndLastInvalidValues { get; set; }
+
     /// <summary>
     /// 123456789 results in "123***789"
     /// </summary>
@@ -278,7 +284,7 @@ public class CustomizedMaskedLogs
     public string? ShowFirstAndLastThreeAndCustomMaskInTheMiddlePreservedLengthIgnored { get; set; }
 }
 ```
-<sup><a href='/src/Destructurama.Attributed.Tests/MaskedAttributeTests.cs#L8-L127' title='Snippet source file'>snippet source</a> | <a href='#snippet-customizedmaskedlogs' title='Start of snippet'>anchor</a></sup>
+<sup><a href='/src/Destructurama.Attributed.Tests/MaskedAttributeTests.cs#L8-L133' title='Snippet source file'>snippet source</a> | <a href='#snippet-customizedmaskedlogs' title='Start of snippet'>anchor</a></sup>
 <!-- endSnippet -->
 
 ## 7. Masking a string property with regular expressions
diff --git a/src/Destructurama.Attributed.Tests/MaskedAttributeTests.cs b/src/Destructurama.Attributed.Tests/MaskedAttributeTests.cs
index 567ee1d..fc53f6f 100644
--- a/src/Destructurama.Attributed.Tests/MaskedAttributeTests.cs
+++ b/src/Destructurama.Attributed.Tests/MaskedAttributeTests.cs
@@ -105,6 +105,12 @@ public class CustomizedMaskedLogs
     [LogMasked(ShowFirst = 3, ShowLast = 3)]
     public string? ShowFirstAndLastThreeAndDefaultMaskInTheMiddle { get; set; }
 
+    /// <summary>
+    /// 123456789 results in "123456789", no mask applied
+    /// </summary>
+    [LogMasked(ShowFirst = -1, ShowLast = -1)]
+    public string? ShowFirstAndLastInvalidValues { get; set; }
+
     /// <summary>
     /// 123456789 results in "123***789"
     /// </summary>
@@ -359,6 +365,25 @@ public void LogMaskedAttribute_Shows_First_NChars_And_Last_NChars_Replaces_Value
         props["ShowFirstAndLastThreeAndDefaultMaskInTheMiddlePreservedLength"].LiteralValue().ShouldBe("123*456");
     }
 
+    [Test]
+    public void LogMaskedAttribute_With_Invalid_Values_Should_Return_Value_As_Is()
+    {
+        // [LogMasked(ShowFirst = -1, ShowLast = -1)]
+        // -> "123456789", no mask applied
+        var customized = new CustomizedMaskedLogs
+        {
+            ShowFirstAndLastInvalidValues = "123456789"
+        };
+
+        var evt = DelegatingSink.Execute(customized);
+
+        var sv = (StructureValue)evt.Properties["Customized"];
+        var props = sv.Properties.ToDictionary(p => p.Name, p => p.Value);
+
+        props.ContainsKey("ShowFirstAndLastInvalidValues").ShouldBeTrue();
+        props["ShowFirstAndLastInvalidValues"].LiteralValue().ShouldBe("123456789");
+    }
+
     [Test]
     public void LogMaskedAttribute_Shows_First_NChars_And_Last_NChars_Then_Replaces_All_Other_Chars_With_Custom_Mask()
     {
diff --git a/src/Destructurama.Attributed/Attributed/LogMaskedAttribute.cs b/src/Destructurama.Attributed/Attributed/LogMaskedAttribute.cs
index 6caaafc..c2b90f0 100644
--- a/src/Destructurama.Attributed/Attributed/LogMaskedAttribute.cs
+++ b/src/Destructurama.Attributed/Attributed/LogMaskedAttribute.cs
@@ -53,15 +53,16 @@ private object FormatMaskedValue(string val)
         if (string.IsNullOrEmpty(val))
             return PreserveLength ? val : Text;
 
-        if (ShowFirst == 0 && ShowLast == 0)
+        return (ShowFirst, ShowLast) switch
         {
-            if (PreserveLength)
-                return new string(Text[0], val.Length);
-
-            return Text;
-        }
+            (0, 0) => PreserveLength ? new string(Text[0], val.Length) : Text,
+            ( > 0, 0) => ShowOnlyFirst(),
+            (0, > 0) => ShowOnlyLast(),
+            ( > 0, > 0) => ShowFirstAndLast(),
+            _ => val
+        };
 
-        if (ShowFirst > 0 && ShowLast == 0)
+        string ShowOnlyFirst()
         {
             var first = val.Substring(0, Math.Min(ShowFirst, val.Length));
 
@@ -73,10 +74,9 @@ private object FormatMaskedValue(string val)
                 mask = new(Text[0], val.Length - ShowFirst);
 
             return first + mask;
-
         }
 
-        if (ShowFirst == 0 && ShowLast > 0)
+        string ShowOnlyLast()
         {
             var last = ShowLast > val.Length ? val : val.Substring(val.Length - ShowLast);
 
@@ -90,7 +90,7 @@ private object FormatMaskedValue(string val)
             return mask + last;
         }
 
-        if (ShowFirst > 0 && ShowLast > 0)
+        string ShowFirstAndLast()
         {
             if (ShowFirst + ShowLast >= val.Length)
                 return val;
@@ -104,8 +104,6 @@ private object FormatMaskedValue(string val)
 
             return first + (mask ?? Text) + last;
         }
-
-        return val;
     }
 
     /// <inheritdoc/>