diff --git a/ChangeLog.md b/ChangeLog.md
index 1267b618e9..bef300d235 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fix [RCS1187](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1187.md) ([#1150](https://github.com/JosefPihrt/Roslynator/pull/1150)).
 - Fix [RCS1056](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1056.md) ([#1154](https://github.com/JosefPihrt/Roslynator/pull/1154)).
+- Fix [RCS1208](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1208.md) ([#1153](https://github.com/JosefPihrt/Roslynator/pull/1153))
 
 ## [4.4.0] - 2023-08-01
 
diff --git a/src/CSharp.Workspaces/CSharp/SyntaxLogicalInverter.cs b/src/CSharp.Workspaces/CSharp/SyntaxLogicalInverter.cs
index e67258375b..e46506796d 100644
--- a/src/CSharp.Workspaces/CSharp/SyntaxLogicalInverter.cs
+++ b/src/CSharp.Workspaces/CSharp/SyntaxLogicalInverter.cs
@@ -128,13 +128,26 @@ private ExpressionSyntax LogicallyInvertImpl(
             case SyntaxKind.IsExpression:
                 {
                     var isExpression = (BinaryExpressionSyntax)expression;
+                    var rightTypeSymbol = (ITypeSymbol)semanticModel.GetSymbol(isExpression.Right, cancellationToken)!;
 
-                    return IsPatternExpression(
-                        isExpression.Left,
-                        isExpression.OperatorToken.WithTrailingTrivia(Space),
-                        UnaryPattern(
-                            Token(SyntaxKind.NotKeyword).WithTrailingTrivia(isExpression.OperatorToken.TrailingTrivia),
-                            TypePattern((TypeSyntax)isExpression.Right)));
+                    TypeSyntax type = rightTypeSymbol.ToTypeSyntax();
+
+                    if (SymbolEqualityComparer.Default.Equals(
+                        semanticModel.GetSpeculativeSymbolInfo(isExpression.SpanStart, isExpression.Right, SpeculativeBindingOption.BindAsExpression).Symbol,
+                        semanticModel.GetSpeculativeSymbolInfo(isExpression.SpanStart, isExpression.Right, SpeculativeBindingOption.BindAsTypeOrNamespace).Symbol))
+                    {
+                        type = type.WithSimplifierAnnotation();
+                    }
+
+                    return (Options.UseNotPattern)
+                        ? IsPatternExpression(
+                            isExpression.Left,
+                            isExpression.OperatorToken.WithTrailingTrivia(Space),
+                            UnaryPattern(
+                                Token(SyntaxKind.NotKeyword)
+                                    .WithTrailingTrivia(isExpression.OperatorToken.TrailingTrivia),
+                                TypePattern(type)))
+                        : DefaultInvert(expression);
                 }
             case SyntaxKind.AsExpression:
                 {
diff --git a/src/Tests/Analyzers.Tests/RCS1208ReduceIfNestingTests.cs b/src/Tests/Analyzers.Tests/RCS1208ReduceIfNestingTests.cs
index 54a9e8298e..a6c5a1d3bd 100644
--- a/src/Tests/Analyzers.Tests/RCS1208ReduceIfNestingTests.cs
+++ b/src/Tests/Analyzers.Tests/RCS1208ReduceIfNestingTests.cs
@@ -50,6 +50,56 @@ void M2()
 ");
     }
 
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.ReduceIfNesting)]
+    public async Task Test_IsWhenIsNotIsInvalid()
+    {
+        await VerifyDiagnosticAndFixAsync(@"
+class X
+{
+}
+
+class C
+{
+    public X X { get; set; }
+
+    C(object o)
+    {
+        [|if|] (o is X)
+        {
+            M2();
+        }
+    }
+
+    void M2()
+    {
+    }
+}
+", @"
+class X
+{
+}
+
+class C
+{
+    public X X { get; set; }
+
+    C(object o)
+    {
+        if (o is not global::X)
+        {
+            return;
+        }
+
+        M2();
+    }
+
+    void M2()
+    {
+    }
+}
+");
+    }
+
     [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.ReduceIfNesting)]
     public async Task Test_WhenParentIsConversionOperator()
     {
@@ -614,6 +664,82 @@ void M2()
     {
     }
 }
+");
+    }
+
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.ReduceIfNesting)]
+    public async Task Test_WhenIsExpressionCsharp8()
+    {
+        await VerifyDiagnosticAndFixAsync(@"
+class C
+{
+    void M(object o)
+    {
+        [|if|] (o is string)
+        {
+            M2();
+        }
+    }
+
+    void M2()
+    {
+    }
+}
+", @"
+class C
+{
+    void M(object o)
+    {
+        if (!(o is string))
+        {
+            return;
+        }
+
+        M2();
+    }
+
+    void M2()
+    {
+    }
+}
+", options: WellKnownCSharpTestOptions.Default_CSharp8);
+    }
+
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.ReduceIfNesting)]
+    public async Task Test_WhenIsExpression()
+    {
+        await VerifyDiagnosticAndFixAsync(@"
+class C
+{
+    void M(object o)
+    {
+        [|if|] (o is string)
+        {
+            M2();
+        }
+    }
+
+    void M2()
+    {
+    }
+}
+", @"
+class C
+{
+    void M(object o)
+    {
+        if (o is not string)
+        {
+            return;
+        }
+
+        M2();
+    }
+
+    void M2()
+    {
+    }
+}
 ");
     }
 }