diff --git a/src/Moq/ISetup.cs b/src/Moq/ISetup.cs
index 03255edba..1e493760c 100644
--- a/src/Moq/ISetup.cs
+++ b/src/Moq/ISetup.cs
@@ -49,7 +49,7 @@ public interface ISetup
         // /// <exception cref="InvalidOperationException">The setup has more than one inner mock.</exception>
         // [Obsolete("Use 'InnerMocks' instead.")]
         // [EditorBrowsable(EditorBrowsableState.Never)]
-        Mock InnerMock { get; }
+        Mock? InnerMock { get; }
 
         // /// <summary>
         // ///   Gets the inner mocks of this setup (if present and known).
diff --git a/src/Moq/Setup.cs b/src/Moq/Setup.cs
index be6f754db..f9030b851 100644
--- a/src/Moq/Setup.cs
+++ b/src/Moq/Setup.cs
@@ -35,7 +35,7 @@ protected Setup(Expression originalExpression, Mock mock, Expectation expectatio
 
         public LambdaExpression Expression => this.expectation.Expression;
 
-        Mock ISetup.InnerMock => this.InnerMocks.SingleOrDefault();
+        Mock? ISetup.InnerMock => this.InnerMocks.SingleOrDefault();
 
         public virtual IEnumerable<Mock> InnerMocks => Enumerable.Empty<Mock>();