diff --git a/lib/typeprof/core/ast/module.rb b/lib/typeprof/core/ast/module.rb
index 8d97aabfd..cf125acce 100644
--- a/lib/typeprof/core/ast/module.rb
+++ b/lib/typeprof/core/ast/module.rb
@@ -89,7 +89,22 @@ class ClassNode < ModuleBaseNode
       def initialize(raw_node, lenv, use_result)
         super(raw_node, lenv, raw_node.constant_path, false, raw_node.body, use_result)
         raw_superclass = raw_node.superclass
-        @superclass_cpath = raw_superclass ? AST.create_node(raw_superclass, lenv) : nil
+        if raw_superclass
+          # In Ruby, the superclass expression is evaluated before the class constant
+          # is created. When the superclass is a bare constant with the same name as
+          # the class being defined (e.g., `class Foo < Foo` inside a module), use the
+          # outer scope to avoid resolving to the class itself.
+          if @static_cpath && lenv.cref.outer &&
+             raw_superclass.type == :constant_read_node &&
+             raw_superclass.name == @static_cpath.last
+            slenv = LocalEnv.new(lenv.file_context, lenv.cref.outer, {}, [])
+            @superclass_cpath = AST.create_node(raw_superclass, slenv)
+          else
+            @superclass_cpath = AST.create_node(raw_superclass, lenv)
+          end
+        else
+          @superclass_cpath = nil
+        end
       end
 
       attr_reader :superclass_cpath
@@ -113,6 +128,21 @@ def undefine0(genv)
 
       def install0(genv)
         @superclass_cpath.install(genv) if @superclass_cpath
+        if @static_cpath && @superclass_cpath
+          const_read = @superclass_cpath.static_ret
+          if const_read && const_read.cpath
+            super_mod = genv.resolve_cpath(const_read.cpath)
+            self_mod = genv.resolve_cpath(@static_cpath)
+            mod = super_mod
+            while mod
+              if mod == self_mod
+                @changes.add_diagnostic(:code_range, "circular inheritance", @superclass_cpath)
+                break
+              end
+              mod = mod.superclass
+            end
+          end
+        end
         super(genv)
       end
     end
diff --git a/scenario/class/circular.rb b/scenario/class/circular.rb
index cfd30da14..5eefeee0c 100644
--- a/scenario/class/circular.rb
+++ b/scenario/class/circular.rb
@@ -16,3 +16,6 @@ class B # failed to identify its superclass
 end
 module M
 end
+
+## diagnostics
+(4,10)-(4,11): circular inheritance
diff --git a/scenario/class/circular_mutual.rb b/scenario/class/circular_mutual.rb
new file mode 100644
index 000000000..9e00aa5b5
--- /dev/null
+++ b/scenario/class/circular_mutual.rb
@@ -0,0 +1,23 @@
+## update
+class Foo
+end
+
+class Bar
+  class Baz < Foo
+  end
+  class Foo < Baz
+  end
+end
+
+## assert
+class Foo
+end
+class Bar
+  class Bar::Baz < Bar::Foo
+  end
+  class Bar::Foo # failed to identify its superclass
+  end
+end
+
+## diagnostics
+(7,14)-(7,17): circular inheritance
diff --git a/scenario/regressions/superclass-self-reference.rb b/scenario/regressions/superclass-self-reference.rb
new file mode 100644
index 000000000..9fa1ecd3f
--- /dev/null
+++ b/scenario/regressions/superclass-self-reference.rb
@@ -0,0 +1,19 @@
+## update: model.rb
+class Foo
+  def value = 1
+end
+
+module Bar
+  class Foo < Foo
+  end
+end
+
+## update: test.rb
+def call
+  Bar::Foo.new.value
+end
+
+## assert: test.rb
+class Object
+  def call: -> Integer
+end