diff --git a/docs/errata/README.md b/docs/errata/README.md
index 7fdde86..b72d36f 100644
--- a/docs/errata/README.md
+++ b/docs/errata/README.md
@@ -2,7 +2,7 @@
 
 If you find any mistakes in the seventh edition, *C# 11 and .NET 7 - Modern Cross-Platform Development Fundamentals*, or if you have suggestions for improvements, then please [raise an issue in this repository](https://github.com/markjprice/cs11dotnet7/issues) or email me at markjprice (at) gmail.com.
 
-[**Errata** (29 items)](errata.md): Typos, tool user interface changes, or mistakes in code that would cause a compilation error that prevents a successful build.
+[**Errata** (30 items)](errata.md): Typos, tool user interface changes, or mistakes in code that would cause a compilation error that prevents a successful build.
 
 [**Improvements** (6 items)](improvements.md): Changes to text or code that would improve the content. These are optional.
 
diff --git a/docs/errata/errata.md b/docs/errata/errata.md
index 79667f7..a9ee96b 100644
--- a/docs/errata/errata.md
+++ b/docs/errata/errata.md
@@ -1,4 +1,4 @@
-**Errata** (29 items)
+**Errata** (30 items)
 
 If you find any mistakes, then please [raise an issue in this repository](https://github.com/markjprice/cs11dotnet7/issues) or email me at markjprice (at) gmail.com.
 
@@ -16,6 +16,7 @@ If you find any mistakes, then please [raise an issue in this repository](https:
 - [Page 166 - Setting a breakpoint and starting debugging - Using Visual Studio 2022](#page-166---setting-a-breakpoint-and-starting-debugging---using-visual-studio-2022)
 - [Page 185 - Creating a class library that needs testing](#page-185---creating-a-class-library-that-needs-testing)
 - [Page 188 - Running unit tests using Visual Studio Code](#page-188---running-unit-tests-using-visual-studio-code)
+- [Page 231 - Requiring properties to be set during instantiation](#page-231---requiring-properties-to-be-set-during-instantiation)
 - [Page 244 - Init-only properties](#page-244---init-only-properties)
 - [Page 258 - Defining and handling events](#page-258---defining-and-handling-events)
 - [Page 272 - Defining struct types](#page-272---defining-struct-types)
@@ -175,6 +176,30 @@ In the "If you are using Visual Studio Code" section, in Step 5, the command in
 
 In Step 1, the project name `CalculatorLibUnitTest` should be `CalculatorLibUnitTests`.
 
+# Page 231 - Requiring properties to be set during instantiation
+
+> Thanks to [Masoud Nazari](https://github.com/MAS-OUD) for raising this [issue on 1 March 2023](https://github.com/markjprice/cs11dotnet7/issues/33).
+
+In Step 1, you are told to add a new class library project named `PacktLibraryModern`. 
+
+In Step 4, in the `PeopleApp` console app project, you are told to create an instance of the `Book` class that is defined in the class library. To do so, you must have added a reference to the `PacktLibraryModern` project. 
+
+In the next edition, I will add steps before Step 4 to remind readers how to do this, as shown below:
+
+*If you are using Visual Studio 2022:*
+- In **Solution Explorer**, select the `PeopleApp` project, navigate to **Project** | **Add Project Reference…**, check the box to select the **PacktLibraryModern** project, and then click **OK**.
+
+*If you are using Visual Studio Code:*
+- Edit `PeopleApp.csproj` to add a project reference to `PacktLibraryModern`, as shown in 
+the following markup:
+```xml
+<ItemGroup>
+  <ProjectReference Include="../PacktLibraryModern/PacktLibraryModern.csproj" />
+</ItemGroup>
+```
+
+- Build the `PeopleApp` project.
+
 # Page 244 - Init-only properties
 
 > Thanks to Bob Molloy for raising this issue via email.