micropython
diff --git a/‎py/builtinimport.c
Lines changed: 16 additions & 4 deletions b/‎py/builtinimport.c
Lines changed: 16 additions & 4 deletions
@@ -372,29 +372,41 @@ STATIC mp_obj_t process_import_at_level(qstr full_mod_name, qstr level_mod_name,
     if (outer_module_obj == MP_OBJ_NULL) {
         DEBUG_printf("Searching for top-level module\n");
 
+        // Always prefer an exact match for any u-prefixed built-in.
+        // e.g. `import utime` bypasses the filesystem.
+        const char *level_mod_name_str = qstr_str(level_mod_name);
+        if (level_mod_name_str[0] == 'u') {
+            module_obj = mp_module_get_builtin(level_mod_name);
+            if (module_obj != MP_OBJ_NULL) {
+                return module_obj;
+            }
+        }
+
         // First module in the dotted-name; search for a directory or file
         // relative to all the locations in sys.path.
-        stat = stat_top_level(full_mod_name, &path);
+        stat = stat_top_level(level_mod_name, &path);
 
         // There's always an implicit "builtin modules" at the end of sys.path.
         if (stat == MP_IMPORT_STAT_NO_EXIST) {
             // Direct match of module name for builtin.
-            module_obj = mp_module_get_builtin(full_mod_name);
+            // e.g. `import pyb` will use builtin unless pyb exists on the filesystem.
+            module_obj = mp_module_get_builtin(level_mod_name);
             if (module_obj != MP_OBJ_NULL) {
                 return module_obj;
             }
 
             #if MICROPY_MODULE_WEAK_LINKS
             // If "foo" was requested, then try "ufoo" as a built-in.
             // (This feature was formerly known as "weak links").
-            qstr umodule_name = make_weak_link_name(&path, full_mod_name);
+            // e.g. `import time` will use builtin time, unless time exists on the filesystem.
+            qstr umodule_name = make_weak_link_name(&path, level_mod_name);
             module_obj = mp_module_get_builtin(umodule_name);
             if (module_obj != MP_OBJ_NULL) {
                 return module_obj;
             }
             #elif MICROPY_PY_SYS
             // Special handling to make `import sys` work even if weak links aren't enabled.
-            if (full_mod_name == MP_QSTR_sys) {
+            if (level_mod_name == MP_QSTR_sys) {
                 return MP_OBJ_FROM_PTR(&mp_module_sys);
             }
             #endif