diff --git a/CHANGELOG.md b/CHANGELOG.md
index dfc6561584..13d27e1f47 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,8 @@ Deprecations:
    - `Castle.Core.Internal.Lock` (class)
    - `Castle.Core.Internal.ILockHolder` (interface)
    - `Castle.Core.Internal.IUpgradeableLockHolder` (interface)
+- You should no longer manually emit types into DynamicProxy's dynamic assembly. For this reason, the following member has been deprecated. (@stakx, #445)
+   - `Castle.DynamicProxy.ModuleScope.DefineType` (method)
 - The proxy type cache in `ModuleScope` should no longer be accessed directly. For this reason, the members listed below have been deprecated. (@stakx, #391)
    - `Castle.DynamicProxy.ModuleScope.Lock` (property)
    - `Castle.DynamicProxy.ModuleScope.GetFromCache` (method)
diff --git a/ref/Castle.Core-net35.cs b/ref/Castle.Core-net35.cs
index 683955f681..45830c8c3c 100644
--- a/ref/Castle.Core-net35.cs
+++ b/ref/Castle.Core-net35.cs
@@ -2647,6 +2647,7 @@ public ModuleScope(bool savePhysicalAssembly, bool disableSignedModule, Castle.D
         public System.Reflection.Emit.ModuleBuilder WeakNamedModule { get; }
         public string WeakNamedModuleDirectory { get; }
         public string WeakNamedModuleName { get; }
+        [System.ObsoleteAttribute("Exposes a component that is intended for internal use only.")]
         public System.Reflection.Emit.TypeBuilder DefineType(bool inSignedModulePreferably, string name, System.Reflection.TypeAttributes flags) { }
         [System.ObsoleteAttribute("Exposes a component that is intended for internal use only.")]
         public System.Type GetFromCache(Castle.DynamicProxy.Generators.CacheKey key) { }
diff --git a/ref/Castle.Core-net40.cs b/ref/Castle.Core-net40.cs
index 8925f59cde..0af1511a6f 100644
--- a/ref/Castle.Core-net40.cs
+++ b/ref/Castle.Core-net40.cs
@@ -2694,6 +2694,7 @@ public ModuleScope(bool savePhysicalAssembly, bool disableSignedModule, Castle.D
         public System.Reflection.Emit.ModuleBuilder WeakNamedModule { get; }
         public string WeakNamedModuleDirectory { get; }
         public string WeakNamedModuleName { get; }
+        [System.ObsoleteAttribute("Exposes a component that is intended for internal use only.")]
         public System.Reflection.Emit.TypeBuilder DefineType(bool inSignedModulePreferably, string name, System.Reflection.TypeAttributes flags) { }
         [System.ObsoleteAttribute("Exposes a component that is intended for internal use only.")]
         public System.Type GetFromCache(Castle.DynamicProxy.Generators.CacheKey key) { }
diff --git a/ref/Castle.Core-net45.cs b/ref/Castle.Core-net45.cs
index 85474a0316..564abab055 100644
--- a/ref/Castle.Core-net45.cs
+++ b/ref/Castle.Core-net45.cs
@@ -2694,6 +2694,7 @@ public ModuleScope(bool savePhysicalAssembly, bool disableSignedModule, Castle.D
         public System.Reflection.Emit.ModuleBuilder WeakNamedModule { get; }
         public string WeakNamedModuleDirectory { get; }
         public string WeakNamedModuleName { get; }
+        [System.ObsoleteAttribute("Exposes a component that is intended for internal use only.")]
         public System.Reflection.Emit.TypeBuilder DefineType(bool inSignedModulePreferably, string name, System.Reflection.TypeAttributes flags) { }
         [System.ObsoleteAttribute("Exposes a component that is intended for internal use only.")]
         public System.Type GetFromCache(Castle.DynamicProxy.Generators.CacheKey key) { }
diff --git a/ref/Castle.Core-netstandard1.3.cs b/ref/Castle.Core-netstandard1.3.cs
index 5ad6decc87..d6a2471e6a 100644
--- a/ref/Castle.Core-netstandard1.3.cs
+++ b/ref/Castle.Core-netstandard1.3.cs
@@ -1543,6 +1543,7 @@ public ModuleScope(bool savePhysicalAssembly, bool disableSignedModule, Castle.D
         public string StrongNamedModuleName { get; }
         public System.Reflection.Emit.ModuleBuilder WeakNamedModule { get; }
         public string WeakNamedModuleName { get; }
+        [System.ObsoleteAttribute("Exposes a component that is intended for internal use only.")]
         public System.Reflection.Emit.TypeBuilder DefineType(bool inSignedModulePreferably, string name, System.Reflection.TypeAttributes flags) { }
         [System.ObsoleteAttribute("Exposes a component that is intended for internal use only.")]
         public System.Type GetFromCache(Castle.DynamicProxy.Generators.CacheKey key) { }
diff --git a/ref/Castle.Core-netstandard1.5.cs b/ref/Castle.Core-netstandard1.5.cs
index fba6d0a371..caabc0f2ab 100644
--- a/ref/Castle.Core-netstandard1.5.cs
+++ b/ref/Castle.Core-netstandard1.5.cs
@@ -1543,6 +1543,7 @@ public ModuleScope(bool savePhysicalAssembly, bool disableSignedModule, Castle.D
         public string StrongNamedModuleName { get; }
         public System.Reflection.Emit.ModuleBuilder WeakNamedModule { get; }
         public string WeakNamedModuleName { get; }
+        [System.ObsoleteAttribute("Exposes a component that is intended for internal use only.")]
         public System.Reflection.Emit.TypeBuilder DefineType(bool inSignedModulePreferably, string name, System.Reflection.TypeAttributes flags) { }
         [System.ObsoleteAttribute("Exposes a component that is intended for internal use only.")]
         public System.Type GetFromCache(Castle.DynamicProxy.Generators.CacheKey key) { }
diff --git a/src/Castle.Core/DynamicProxy/ModuleScope.cs b/src/Castle.Core/DynamicProxy/ModuleScope.cs
index e9f1a47b42..2ae9de52dc 100644
--- a/src/Castle.Core/DynamicProxy/ModuleScope.cs
+++ b/src/Castle.Core/DynamicProxy/ModuleScope.cs
@@ -573,6 +573,8 @@ public void LoadAssemblyIntoCache(Assembly assembly)
 		}
 #endif
 
+		[Obsolete("Exposes a component that is intended for internal use only.")] // TODO: Redeclare this method as `internal`.
+		[EditorBrowsable(EditorBrowsableState.Never)]
 		public TypeBuilder DefineType(bool inSignedModulePreferably, string name, TypeAttributes flags)
 		{
 			var module = ObtainDynamicModule(disableSignedModule == false && inSignedModulePreferably);