diff --git a/Lib/importlib/_bootstrap.py b/Lib/importlib/_bootstrap.py
--- a/Lib/importlib/_bootstrap.py
+++ b/Lib/importlib/_bootstrap.py
@@ -19,6 +19,7 @@ work. One should use importlib as the pu
 
 # Bootstrap-related code ######################################################
 
+import time
 CASE_INSENSITIVE_PLATFORMS = 'win', 'cygwin', 'darwin'
 
 
@@ -763,20 +764,24 @@ class _FileFinder:
         self._path_mtime = -1
         self._path_cache = set()
         self._cache_refresh = 0
+        self._last_time = 0.0
 
     def find_module(self, fullname):
         """Try to find a loader for the specified module."""
         tail_module = fullname.rpartition('.')[2]
         if _relax_case():
             tail_module = tail_module.lower()
-        try:
-            mtime = _os.stat(self.path).st_mtime
-        except OSError:
-            mtime = -1
-        if mtime != self._path_mtime or _cache_refresh != self._cache_refresh:
-            self._fill_cache()
-            self._path_mtime = mtime
-            self._cache_refresh = _cache_refresh
+        now = time.time()
+        if now > self._last_time + 1:
+            self._last_time = now
+            try:
+                mtime = _os.stat(self.path).st_mtime
+            except OSError:
+                mtime = -1
+            if mtime != self._path_mtime or _cache_refresh != self._cache_refresh:
+                self._fill_cache()
+                self._path_mtime = mtime
+                self._cache_refresh = _cache_refresh
         cache = self._path_cache
         if tail_module in cache:
             base_path = _path_join(self.path, tail_module)