diff --git a/tests/import/builtin_ext.py b/tests/import/builtin_ext.py
new file mode 100644
index 0000000000..dd8f95cbc1
--- /dev/null
+++ b/tests/import/builtin_ext.py
@@ -0,0 +1,36 @@
+import sys
+
+print(sys, hasattr(sys, "__file__"))
+
+sys.path.clear()
+sys.path.append("ext")
+
+# All three should only get builtins, despite sys.py, usys.py, and
+# micropython.py being in the path.
+import micropython
+
+print(micropython, hasattr(micropython, "__file__"))
+import sys
+
+print(sys, hasattr(sys, "__file__"))
+import usys
+
+print(usys, hasattr(usys, "__file__"))
+
+# This should get os.py, which uses uos to get the builtin.
+import os
+
+print(os, hasattr(os, "__file__"), os.sep, os.extra)
+
+# This should get time.py, which uses empty sys.path to get the builtin.
+import time
+
+print(time, hasattr(time, "__file__"), time.sleep, time.extra)
+
+# These should get the builtins.
+import uos
+
+print(uos, hasattr(uos, "__file__"), hasattr(uos, "extra"))
+import utime
+
+print(utime, hasattr(utime, "__file__"), hasattr(utime, "extra"))
diff --git a/tests/import/builtin_ext.py.exp b/tests/import/builtin_ext.py.exp
new file mode 100644
index 0000000000..08496e14b7
--- /dev/null
+++ b/tests/import/builtin_ext.py.exp
@@ -0,0 +1,10 @@
+<module 'sys'> False
+<module 'micropython'> False
+<module 'sys'> False
+<module 'sys'> False
+os from filesystem
+<module 'os' from 'ext/os.py'> True / 1
+time from filesystem
+<module 'time' from 'ext/time.py'> True <function> 1
+<module 'uos'> False False
+<module 'utime'> False False
diff --git a/tests/import/ext/micropython.py b/tests/import/ext/micropython.py
new file mode 100644
index 0000000000..88c8b770e1
--- /dev/null
+++ b/tests/import/ext/micropython.py
@@ -0,0 +1,2 @@
+# micropython is always builtin and cannot be overriden by the filesystem.
+print("ERROR: micropython from filesystem")
diff --git a/tests/import/ext/os.py b/tests/import/ext/os.py
new file mode 100644
index 0000000000..e1448805d0
--- /dev/null
+++ b/tests/import/ext/os.py
@@ -0,0 +1,5 @@
+print("os from filesystem")
+
+from uos import *
+
+extra = 1
diff --git a/tests/import/ext/sys.py b/tests/import/ext/sys.py
new file mode 100644
index 0000000000..71ee633e11
--- /dev/null
+++ b/tests/import/ext/sys.py
@@ -0,0 +1,2 @@
+# sys is always builtin and cannot be overriden by the filesystem.
+print("ERROR: sys from filesystem")
diff --git a/tests/import/ext/time.py b/tests/import/ext/time.py
new file mode 100644
index 0000000000..6f2d4a42c0
--- /dev/null
+++ b/tests/import/ext/time.py
@@ -0,0 +1,14 @@
+print("time from filesystem")
+
+# Tests the CPython-compatible / non-u-prefix way of forcing a builtin
+# import.
+import sys
+
+_path = sys.path[:]
+sys.path.clear()
+from time import *
+
+sys.path.extend(_path)
+del _path
+
+extra = 1
diff --git a/tests/import/ext/usys.py b/tests/import/ext/usys.py
new file mode 100644
index 0000000000..d7629a4499
--- /dev/null
+++ b/tests/import/ext/usys.py
@@ -0,0 +1,3 @@
+# usys (and any u-prefix) is always builtin and cannot be overriden by the
+# filesystem.
+print("ERROR: usys from filesystem")