diff --git a/spec/compiler/semantic/macro_spec.cr b/spec/compiler/semantic/macro_spec.cr
index fdc71fdfc01f..7868840cc73a 100644
--- a/spec/compiler/semantic/macro_spec.cr
+++ b/spec/compiler/semantic/macro_spec.cr
@@ -775,6 +775,22 @@ describe "Semantic: macro" do
       )) { int32.metaclass }
   end
 
+  it "finds generic type argument of included module with self" do
+    assert_type(%(
+      module Bar(T)
+        def t
+          {{ T }}
+        end
+      end
+
+      class Foo(U)
+        include Bar(self)
+      end
+
+      Foo(Int32).new.t
+      )) { generic_class("Foo", int32).metaclass }
+  end
+
   it "finds free type vars" do
     assert_type(%(
       module Foo(T)
diff --git a/spec/compiler/semantic/module_spec.cr b/spec/compiler/semantic/module_spec.cr
index 35c49a9d5d9b..e5fc5cab4c18 100644
--- a/spec/compiler/semantic/module_spec.cr
+++ b/spec/compiler/semantic/module_spec.cr
@@ -226,7 +226,115 @@ describe "Semantic: module" do
         end
       end
 
-      class Baz(X)
+      class Bar(U)
+        include Foo(self)
+      end
+
+      Bar(Int32).new.foo
+      ") { generic_class("Bar", int32).metaclass }
+  end
+
+  it "includes generic module with self, and inherits it" do
+    assert_type("
+      module Foo(T)
+        def foo
+          T
+        end
+      end
+
+      class Bar(U)
+        include Foo(self)
+      end
+
+      class Baz < Bar(Int32)
+      end
+
+      Baz.new.foo
+      ") { types["Baz"].metaclass }
+  end
+
+  it "includes generic module with self (check argument type, success)" do
+    assert_type("
+      module Foo(T)
+        def foo(x : T)
+          x
+        end
+      end
+
+      class Bar(U)
+        include Foo(self)
+      end
+
+      Bar(Int32).new.foo Bar(Int32).new
+      ") { generic_class("Bar", int32) }
+  end
+
+  it "includes generic module with self (check argument superclass type, success)" do
+    assert_type("
+      module Foo(T)
+        def foo(x : T)
+          x
+        end
+      end
+
+      class Bar(U)
+        include Foo(self)
+      end
+
+      class Baz < Bar(Int32)
+      end
+
+      Bar(Int32).new.foo Baz.new
+      ") { types["Baz"] }
+  end
+
+  it "includes generic module with self (check argument type, error)" do
+    assert_error "
+      module Foo(T)
+        def foo(x : T)
+          x
+        end
+      end
+
+      class Bar(U)
+        include Foo(self)
+      end
+
+      class Baz1 < Bar(Int32)
+      end
+
+      class Baz2 < Bar(Int32)
+      end
+
+      Baz1.new.foo Baz2.new
+      ", "no overload matches"
+  end
+
+  it "includes generic module with self (check argument superclass type, error)" do
+    assert_error "
+      module Foo(T)
+        def foo(x : T)
+          x
+        end
+      end
+
+      class Bar(U)
+        include Foo(self)
+      end
+
+      class Baz < Bar(Int32)
+      end
+
+      Baz.new.foo Bar(Int32).new
+      ", "no overload matches"
+  end
+
+  it "includes generic module with self (check return type, success)" do
+    assert_type("
+      module Foo(T)
+        def foo : T
+          Bar(Int32).new
+        end
       end
 
       class Bar(U)
@@ -234,7 +342,67 @@ describe "Semantic: module" do
       end
 
       Bar(Int32).new.foo
-      ") { generic_class("Bar", int32).metaclass }
+      ") { generic_class("Bar", int32) }
+  end
+
+  it "includes generic module with self (check return subclass type, success)" do
+    assert_type("
+      module Foo(T)
+        def foo : T
+          Baz.new
+        end
+      end
+
+      class Bar(U)
+        include Foo(self)
+      end
+
+      class Baz < Bar(Int32)
+      end
+
+      Bar(Int32).new.foo
+      ") { types["Baz"] }
+  end
+
+  it "includes generic module with self (check return type, error)" do
+    assert_error "
+      module Foo(T)
+        def foo : T
+          Bar(Int32).new
+        end
+      end
+
+      class Bar(U)
+        include Foo(self)
+      end
+
+      class Baz < Bar(Int32)
+      end
+
+      Baz.new.foo
+      ", "type must be Baz, not Bar(Int32)"
+  end
+
+  it "includes generic module with self (check return subclass type, error)" do
+    assert_error "
+      module Foo(T)
+        def foo : T
+          Baz2.new
+        end
+      end
+
+      class Bar(U)
+        include Foo(self)
+      end
+
+      class Baz1 < Bar(Int32)
+      end
+
+      class Baz2 < Bar(Int32)
+      end
+
+      Baz1.new.foo
+      ", "type must be Baz1, not Baz2"
   end
 
   it "includes module but can't access metaclass methods" do
diff --git a/src/compiler/crystal/macros/interpreter.cr b/src/compiler/crystal/macros/interpreter.cr
index feb183050564..fc39e4999383 100644
--- a/src/compiler/crystal/macros/interpreter.cr
+++ b/src/compiler/crystal/macros/interpreter.cr
@@ -418,6 +418,9 @@ module Crystal
         end
 
         TypeNode.new(matched_type)
+      when Self
+        target = @scope == @program.class_type ? @scope : @scope.instance_type
+        TypeNode.new(target)
       when ASTNode
         matched_type
       else
diff --git a/src/compiler/crystal/semantic/main_visitor.cr b/src/compiler/crystal/semantic/main_visitor.cr
index 239944fb3126..0b832baa3537 100644
--- a/src/compiler/crystal/semantic/main_visitor.cr
+++ b/src/compiler/crystal/semantic/main_visitor.cr
@@ -167,6 +167,8 @@ module Crystal
         node.bind_to type.value
       when Type
         node.type = check_type_in_type_args(type.remove_alias_if_simple)
+      when Self
+        node.type = check_type_in_type_args(the_self(node).remove_alias_if_simple)
       when ASTNode
         type.accept self unless type.type?
         node.syntax_replacement = type
@@ -300,12 +302,7 @@ module Crystal
     end
 
     def visit(node : Self)
-      the_self = (@scope || current_type)
-      if the_self.is_a?(Program)
-        node.raise "there's no self in this scope"
-      end
-
-      node.type = the_self.instance_type
+      node.type = the_self(node).instance_type
     end
 
     def visit(node : Var)
@@ -3100,6 +3097,14 @@ module Crystal
       end
     end
 
+    def the_self(node)
+      the_self = (@scope || current_type)
+      if the_self.is_a?(Program)
+        node.raise "there's no self in this scope"
+      end
+      the_self
+    end
+
     def visit(node : When | Unless | Until | MacroLiteral | OpAssign)
       raise "Bug: #{node.class_desc} node '#{node}' (#{node.location}) should have been eliminated in normalize"
     end
diff --git a/src/compiler/crystal/semantic/semantic_visitor.cr b/src/compiler/crystal/semantic/semantic_visitor.cr
index 22ebbf685882..179d88886bfc 100644
--- a/src/compiler/crystal/semantic/semantic_visitor.cr
+++ b/src/compiler/crystal/semantic/semantic_visitor.cr
@@ -214,8 +214,8 @@ abstract class Crystal::SemanticVisitor < Crystal::Visitor
     end
   end
 
-  def lookup_type(node : ASTNode, free_vars = nil)
-    current_type.lookup_type(node, free_vars: free_vars, allow_typeof: false)
+  def lookup_type(node : ASTNode, free_vars = nil, lazy_self = false)
+    current_type.lookup_type(node, free_vars: free_vars, allow_typeof: false, lazy_self: lazy_self)
   end
 
   def check_outside_exp(node, op)
diff --git a/src/compiler/crystal/semantic/top_level_visitor.cr b/src/compiler/crystal/semantic/top_level_visitor.cr
index bda70cf17b4c..0a0e986e9be9 100644
--- a/src/compiler/crystal/semantic/top_level_visitor.cr
+++ b/src/compiler/crystal/semantic/top_level_visitor.cr
@@ -811,7 +811,7 @@ class Crystal::TopLevelVisitor < Crystal::SemanticVisitor
   def include_in(current_type, node, kind)
     node_name = node.name
 
-    type = lookup_type(node_name)
+    type = lookup_type(node_name, lazy_self: true)
     case type
     when GenericModuleType
       node.raise "wrong number of type vars for #{type} (given 0, expected #{type.type_vars.size})"
diff --git a/src/compiler/crystal/semantic/type_lookup.cr b/src/compiler/crystal/semantic/type_lookup.cr
index ed6c23025cf4..26c2d61a54cd 100644
--- a/src/compiler/crystal/semantic/type_lookup.cr
+++ b/src/compiler/crystal/semantic/type_lookup.cr
@@ -38,28 +38,28 @@ class Crystal::Type
   # ```
   #
   # If `self` is `Foo` and `Bar(Baz)` is given, the result will be `Foo::Bar(Baz)`.
-  def lookup_type(node : ASTNode, self_type = self.instance_type, allow_typeof = true, free_vars : Hash(String, TypeVar)? = nil) : Type
-    TypeLookup.new(self, self_type, true, allow_typeof, free_vars).lookup(node).not_nil!
+  def lookup_type(node : ASTNode, self_type = self.instance_type, allow_typeof = true, lazy_self = false, free_vars : Hash(String, TypeVar)? = nil) : Type
+    TypeLookup.new(self, self_type, true, allow_typeof, lazy_self, free_vars).lookup(node).not_nil!
   end
 
   # Similar to `lookup_type`, but returns `nil` if a type can't be found.
-  def lookup_type?(node : ASTNode, self_type = self.instance_type, allow_typeof = true, free_vars : Hash(String, TypeVar)? = nil) : Type?
-    TypeLookup.new(self, self_type, false, allow_typeof, free_vars).lookup(node)
+  def lookup_type?(node : ASTNode, self_type = self.instance_type, allow_typeof = true, lazy_self = false, free_vars : Hash(String, TypeVar)? = nil) : Type?
+    TypeLookup.new(self, self_type, false, allow_typeof, lazy_self, free_vars).lookup(node)
   end
 
   # Similar to `lookup_type`, but the result might also be an ASTNode, for example when
   # looking `N` relative to a StaticArray.
   def lookup_type_var(node : Path, free_vars : Hash(String, TypeVar)? = nil) : Type | ASTNode
-    TypeLookup.new(self, self.instance_type, true, false, free_vars).lookup_type_var(node).not_nil!
+    TypeLookup.new(self, self.instance_type, true, false, false, free_vars).lookup_type_var(node).not_nil!
   end
 
   # Similar to `lookup_type_var`, but might return `nil`.
   def lookup_type_var?(node : Path, free_vars : Hash(String, TypeVar)? = nil, raise = false) : Type | ASTNode | Nil
-    TypeLookup.new(self, self.instance_type, raise, false, free_vars).lookup_type_var?(node)
+    TypeLookup.new(self, self.instance_type, raise, false, false, free_vars).lookup_type_var?(node)
   end
 
   private struct TypeLookup
-    def initialize(@root : Type, @self_type : Type, @raise : Bool, @allow_typeof : Bool, @free_vars : Hash(String, TypeVar)? = nil)
+    def initialize(@root : Type, @self_type : Type, @raise : Bool, @allow_typeof : Bool, @lazy_self : Bool, @free_vars : Hash(String, TypeVar)? = nil)
       @in_generic_args = 0
 
       # If we are looking types inside a non-instantiated generic type,
@@ -84,6 +84,8 @@ class Crystal::Type
         node.raise "#{type_var} is not a type, it's a constant"
       when Type
         return type_var
+      when Self
+        return lookup(type_var)
       end
 
       if @raise
@@ -211,8 +213,14 @@ class Crystal::Type
       type_vars = Array(TypeVar).new(node.type_vars.size + 1)
       node.type_vars.each do |type_var|
         case type_var
+        when Self
+          if @lazy_self
+            type_vars << type_var
+            next
+          end
         when NumberLiteral
           type_vars << type_var
+          next
         when Splat
           type = in_generic_args { lookup(type_var.exp) }
           return if !@raise && !type
@@ -230,37 +238,38 @@ class Crystal::Type
 
             type_var.raise "can only splat tuple type, not #{splat_type}"
           end
-        else
-          # Check the case of T resolving to a number
-          if type_var.is_a?(Path) && type_var.names.size == 1
-            type = @root.lookup_path(type_var)
-            case type
-            when Const
-              interpreter = MathInterpreter.new(@root)
-              begin
-                num = interpreter.interpret(type.value)
-                type_vars << NumberLiteral.new(num)
-              rescue ex : Crystal::Exception
-                type_var.raise "expanding constant value for a number value", inner: ex
-              end
-              next
-            when ASTNode
-              type_vars << type
-              next
+          next
+        end
+
+        # Check the case of T resolving to a number
+        if type_var.is_a?(Path) && type_var.names.size == 1
+          type = @root.lookup_path(type_var)
+          case type
+          when Const
+            interpreter = MathInterpreter.new(@root)
+            begin
+              num = interpreter.interpret(type.value)
+              type_vars << NumberLiteral.new(num)
+            rescue ex : Crystal::Exception
+              type_var.raise "expanding constant value for a number value", inner: ex
             end
+            next
+            # when ASTNode
+            #   type_vars << type
+            #   next
           end
+        end
 
-          type = in_generic_args { lookup(type_var) }
-          return if !@raise && !type
-          type = type.not_nil!
-
-          case instance_type
-          when GenericUnionType, PointerType, StaticArrayType, TupleType, ProcType
-            check_type_allowed_in_generics(type_var, type, "can't use #{type} as a generic type argument")
-          end
+        type = in_generic_args { lookup(type_var) }
+        return if !@raise && !type
+        type = type.not_nil!
 
-          type_vars << type.virtual_type
+        case instance_type
+        when GenericUnionType, PointerType, StaticArrayType, TupleType, ProcType
+          check_type_allowed_in_generics(type_var, type, "can't use #{type} as a generic type argument")
         end
+
+        type_vars << type.virtual_type
       end
 
       begin