diff --git a/Core/BkwdComp/System.Collections.Generic.PreNet45.cs b/Core/BkwdComp/System.Collections.Generic.PreNet45.cs
index 7ddc04e9..7daa9aa2 100644
--- a/Core/BkwdComp/System.Collections.Generic.PreNet45.cs
+++ b/Core/BkwdComp/System.Collections.Generic.PreNet45.cs
@@ -11,6 +11,40 @@ namespace System.Collections.Generic
 		int Count { get; }
 	}
 
+	/// <summary>Represents a generic read-only collection of key/value pairs.</summary>
+	/// <typeparam name="TKey">The type of keys in the read-only dictionary.</typeparam>
+	/// <typeparam name="TValue">The type of values in the read-only dictionary.</typeparam>
+	public interface IReadOnlyDictionary<TKey, TValue> : IReadOnlyCollection<KeyValuePair<TKey, TValue>>
+	{
+		/// <summary>Determines whether the read-only dictionary contains an element that has the specified key.</summary>
+		/// <param name="key">The key to locate.</param>
+		/// <returns>
+		/// <see langword="true"/> if the read-only dictionary contains an element that has the specified key; otherwise, <see langword="false"/>.
+		/// </returns>
+		bool ContainsKey(TKey key);
+		/// <summary>Gets the value that is associated with the specified key.</summary>
+		/// <param name="key">The key to locate.</param>
+		/// <param name="value">
+		/// When this method returns, the value associated with the specified key, if the key is found; otherwise, the default value for the
+		/// type of the <paramref name="value"/> parameter. This parameter is passed uninitialized.
+		/// </param>
+		/// <returns>
+		/// <see langword="true"/> if the object that implements the <see cref="IReadOnlyDictionary{TKey, TValue}"/> interface contains an
+		/// element that has the specified key; otherwise, <see langword="false"/>.
+		/// </returns>
+		bool TryGetValue(TKey key, out TValue value);
+		/// <summary>Gets the element that has the specified key in the read-only dictionary.</summary>
+		/// <value>The key to locate.</value>
+		/// <returns>The element that has the specified key in the read-only dictionary.</returns>
+		TValue this[TKey key] { get; }
+		/// <summary>Gets an enumerable collection that contains the keys in the read-only dictionary.</summary>
+		/// <value>An enumerable collection that contains the keys in the read-only dictionary.</value>
+		IEnumerable<TKey> Keys { get; }
+		/// <summary>Gets an enumerable collection that contains the values in the read-only dictionary.</summary>
+		/// <value>An enumerable collection that contains the values in the read-only dictionary.</value>
+		IEnumerable<TValue> Values { get; }
+	}
+
 	/// <summary>Represents a read-only collection of elements that can be accessed by index.</summary>
 	/// <typeparam name="T">The type of elements in the read-only list.</typeparam>
 	/// <seealso cref="System.Collections.Generic.IReadOnlyCollection{T}"/>