diff --git a/src/Microsoft.CodeAnalysis.NetAnalyzers/src/Microsoft.CodeAnalysis.NetAnalyzers/Microsoft.CodeQuality.Analyzers/ApiDesignGuidelines/NestedTypesShouldNotBeVisible.cs b/src/Microsoft.CodeAnalysis.NetAnalyzers/src/Microsoft.CodeAnalysis.NetAnalyzers/Microsoft.CodeQuality.Analyzers/ApiDesignGuidelines/NestedTypesShouldNotBeVisible.cs
index 55e53fff08df..cacdeb61622e 100644
--- a/src/Microsoft.CodeAnalysis.NetAnalyzers/src/Microsoft.CodeAnalysis.NetAnalyzers/Microsoft.CodeQuality.Analyzers/ApiDesignGuidelines/NestedTypesShouldNotBeVisible.cs
+++ b/src/Microsoft.CodeAnalysis.NetAnalyzers/src/Microsoft.CodeAnalysis.NetAnalyzers/Microsoft.CodeQuality.Analyzers/ApiDesignGuidelines/NestedTypesShouldNotBeVisible.cs
@@ -76,6 +76,12 @@ public override void Initialize(AnalysisContext context)
                                 return;
                             }
 
+                            // Do not report diagnostic for extension members
+                            if (nestedType.TypeKind == ITypeSymbolExtensions.ExtensionTypeKind)
+                            {
+                                return;
+                            }
+
                             // The Framework Design Guidelines (see 4.9 Nested Types) say that it is okay
                             // to expose nested types for advanced customization and subclassing scenarios,
                             // so, following FxCop's implementation of this rule, we allow protected and
@@ -148,4 +154,4 @@ private static bool IsDataSetSpecialCase(
                 dataRowType != null && nestedTypeBases.Contains(dataRowType);
         }
     }
-}
\ No newline at end of file
+}