diff --git a/csharp/src/Google.Protobuf/Reflection/EnumDescriptor.cs b/csharp/src/Google.Protobuf/Reflection/EnumDescriptor.cs
index 6d0925475c..795a95feeb 100644
--- a/csharp/src/Google.Protobuf/Reflection/EnumDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/EnumDescriptor.cs
@@ -133,6 +133,7 @@ namespace Google.Protobuf.Reflection
 
         /// <summary>
         /// The <c>EnumOptions</c>, defined in <c>descriptor.proto</c>.
+        /// If the options message is not present (=there are no options), <c>null</c> is returned.
         /// Custom options can be retrieved as extensions of the returned message.
         /// NOTE: A defensive copy is created each time this property is retrieved.
         /// </summary>
diff --git a/csharp/src/Google.Protobuf/Reflection/EnumValueDescriptor.cs b/csharp/src/Google.Protobuf/Reflection/EnumValueDescriptor.cs
index 19daec8eb8..291ab8c58f 100644
--- a/csharp/src/Google.Protobuf/Reflection/EnumValueDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/EnumValueDescriptor.cs
@@ -78,6 +78,7 @@ namespace Google.Protobuf.Reflection
 
         /// <summary>
         /// The <c>EnumValueOptions</c>, defined in <c>descriptor.proto</c>.
+        /// If the options message is not present (=there are no options), <c>null</c> is returned.
         /// Custom options can be retrieved as extensions of the returned message.
         /// NOTE: A defensive copy is created each time this property is retrieved.
         /// </summary>
diff --git a/csharp/src/Google.Protobuf/Reflection/FieldDescriptor.cs b/csharp/src/Google.Protobuf/Reflection/FieldDescriptor.cs
index 6f8c2aec46..6ce606a3df 100644
--- a/csharp/src/Google.Protobuf/Reflection/FieldDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/FieldDescriptor.cs
@@ -309,6 +309,7 @@ namespace Google.Protobuf.Reflection
 
         /// <summary>
         /// The <c>FieldOptions</c>, defined in <c>descriptor.proto</c>.
+        /// If the options message is not present (=there are no options), <c>null</c> is returned.
         /// Custom options can be retrieved as extensions of the returned message.
         /// NOTE: A defensive copy is created each time this property is retrieved.
         /// </summary>
diff --git a/csharp/src/Google.Protobuf/Reflection/FileDescriptor.cs b/csharp/src/Google.Protobuf/Reflection/FileDescriptor.cs
index b3dab3a688..9b298935da 100644
--- a/csharp/src/Google.Protobuf/Reflection/FileDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/FileDescriptor.cs
@@ -552,6 +552,7 @@ namespace Google.Protobuf.Reflection
 
         /// <summary>
         /// The <c>FileOptions</c>, defined in <c>descriptor.proto</c>.
+        /// If the options message is not present (=there are no options), <c>null</c> is returned.
         /// Custom options can be retrieved as extensions of the returned message.
         /// NOTE: A defensive copy is created each time this property is retrieved.
         /// </summary>
diff --git a/csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs b/csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs
index 0a1d352153..9746bc89e4 100644
--- a/csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs
@@ -292,6 +292,7 @@ namespace Google.Protobuf.Reflection
 
         /// <summary>
         /// The <c>MessageOptions</c>, defined in <c>descriptor.proto</c>.
+        /// If the options message is not present (=there are no options), <c>null</c> is returned.
         /// Custom options can be retrieved as extensions of the returned message.
         /// NOTE: A defensive copy is created each time this property is retrieved.
         /// </summary>
diff --git a/csharp/src/Google.Protobuf/Reflection/MethodDescriptor.cs b/csharp/src/Google.Protobuf/Reflection/MethodDescriptor.cs
index b42d454f84..b7c426d916 100644
--- a/csharp/src/Google.Protobuf/Reflection/MethodDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/MethodDescriptor.cs
@@ -78,6 +78,7 @@ namespace Google.Protobuf.Reflection
 
         /// <summary>
         /// The <c>MethodOptions</c>, defined in <c>descriptor.proto</c>.
+        /// If the options message is not present (=there are no options), <c>null</c> is returned.
         /// Custom options can be retrieved as extensions of the returned message.
         /// NOTE: A defensive copy is created each time this property is retrieved.
         /// </summary>
diff --git a/csharp/src/Google.Protobuf/Reflection/OneofDescriptor.cs b/csharp/src/Google.Protobuf/Reflection/OneofDescriptor.cs
index d959e078eb..302e66e232 100644
--- a/csharp/src/Google.Protobuf/Reflection/OneofDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/OneofDescriptor.cs
@@ -122,6 +122,7 @@ namespace Google.Protobuf.Reflection
 
         /// <summary>
         /// The <c>OneofOptions</c>, defined in <c>descriptor.proto</c>.
+        /// If the options message is not present (=there are no options), <c>null</c> is returned.
         /// Custom options can be retrieved as extensions of the returned message.
         /// NOTE: A defensive copy is created each time this property is retrieved.
         /// </summary>
diff --git a/csharp/src/Google.Protobuf/Reflection/ServiceDescriptor.cs b/csharp/src/Google.Protobuf/Reflection/ServiceDescriptor.cs
index b56e157de8..f478db05ec 100644
--- a/csharp/src/Google.Protobuf/Reflection/ServiceDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/ServiceDescriptor.cs
@@ -99,6 +99,7 @@ namespace Google.Protobuf.Reflection
 
         /// <summary>
         /// The <c>ServiceOptions</c>, defined in <c>descriptor.proto</c>.
+        /// If the options message is not present (=there are no options), <c>null</c> is returned.
         /// Custom options can be retrieved as extensions of the returned message.
         /// NOTE: A defensive copy is created each time this property is retrieved.
         /// </summary>