diff --git a/tests/functional/codegen/modules/test_interface_imports.py b/tests/functional/codegen/modules/test_interface_imports.py
index 6db08f77a7..c0fae6496c 100644
--- a/tests/functional/codegen/modules/test_interface_imports.py
+++ b/tests/functional/codegen/modules/test_interface_imports.py
@@ -29,3 +29,32 @@ def test_foo(s: ifaces.IFoo) -> bool:
     c = get_contract(contract, input_bundle=input_bundle)
 
     assert c.test_foo(foo.address) is True
+
+
+def test_import_interface_types_stability(make_input_bundle, get_contract):
+    lib1 = """
+from ethereum.ercs import IERC20
+    """
+    lib2 = """
+from ethereum.ercs import IERC20
+    """
+
+    main = """
+import lib1
+import lib2
+
+from ethereum.ercs import IERC20
+
+@external
+def foo() -> bool:
+    # check that this typechecks both directions
+    a: lib1.IERC20 = IERC20(msg.sender)
+    b: lib2.IERC20 = IERC20(msg.sender)
+
+    # return the equality so we can sanity check it
+    return a == b
+    """
+    input_bundle = make_input_bundle({"lib1.vy": lib1, "lib2.vy": lib2})
+    c = get_contract(main, input_bundle=input_bundle)
+
+    assert c.foo() is True
diff --git a/vyper/semantics/analysis/module.py b/vyper/semantics/analysis/module.py
index cb1dc8430f..dd7546732a 100644
--- a/vyper/semantics/analysis/module.py
+++ b/vyper/semantics/analysis/module.py
@@ -10,6 +10,7 @@
     FileInput,
     FilesystemInputBundle,
     InputBundle,
+    PathLike,
 )
 from vyper.evm.opcodes import version_check
 from vyper.exceptions import (
@@ -398,7 +399,7 @@ def _ast_from_file(self, file: FileInput) -> vy_ast.Module:
         # two ASTs produced from the same source
         ast_of = self.input_bundle._cache._ast_of
         if file.source_id not in ast_of:
-            ast_of[file.source_id] = _parse_and_fold_ast(file)
+            ast_of[file.source_id] = _parse_ast(file)
 
         return ast_of[file.source_id]
 
@@ -870,7 +871,7 @@ def _load_import_helper(
         raise ModuleNotFound(module_str, hint=hint) from err
 
 
-def _parse_and_fold_ast(file: FileInput) -> vy_ast.Module:
+def _parse_ast(file: FileInput) -> vy_ast.Module:
     module_path = file.resolved_path  # for error messages
     try:
         # try to get a relative path, to simplify the error message
@@ -910,6 +911,9 @@ def _is_builtin(module_str):
     return any(module_str.startswith(prefix) for prefix in BUILTIN_PREFIXES)
 
 
+_builtins_cache: dict[PathLike, tuple[CompilerInput, ModuleT]] = {}
+
+
 def _load_builtin_import(level: int, module_str: str) -> tuple[CompilerInput, InterfaceT]:
     if not _is_builtin(module_str):
         raise ModuleNotFound(module_str)
@@ -933,6 +937,13 @@ def _load_builtin_import(level: int, module_str: str) -> tuple[CompilerInput, In
 
     path = _import_to_path(level, remapped_module).with_suffix(".vyi")
 
+    # builtins are globally the same, so we can safely cache them
+    # (it is also *correct* to cache them, so that types defined in builtins
+    # compare correctly using pointer-equality.)
+    if path in _builtins_cache:
+        file, module_t = _builtins_cache[path]
+        return file, module_t.interface
+
     try:
         file = input_bundle.load_file(path)
         assert isinstance(file, FileInput)  # mypy hint
@@ -946,9 +957,10 @@ def _load_builtin_import(level: int, module_str: str) -> tuple[CompilerInput, In
             hint = f"try renaming `{module_prefix}` to `I{module_prefix}`"
         raise ModuleNotFound(module_str, hint=hint) from e
 
-    # TODO: it might be good to cache this computation
-    interface_ast = _parse_and_fold_ast(file)
+    interface_ast = _parse_ast(file)
 
     with override_global_namespace(Namespace()):
         module_t = _analyze_module_r(interface_ast, input_bundle, ImportGraph(), is_interface=True)
+
+    _builtins_cache[path] = file, module_t
     return file, module_t.interface
diff --git a/vyper/semantics/types/module.py b/vyper/semantics/types/module.py
index 51d55a167e..cac9b63be5 100644
--- a/vyper/semantics/types/module.py
+++ b/vyper/semantics/types/module.py
@@ -127,7 +127,7 @@ def _is_function_implemented(fn_name, fn_type):
                 continue
 
             if not _is_function_implemented(name, type_):
-                unimplemented.append(name)
+                unimplemented.append(type_._pp_signature)
 
         if len(unimplemented) > 0:
             # TODO: improve the error message for cases where the