diff --git a/python/ray/__init__.py b/python/ray/__init__.py
index c631fb069..10918f0d0 100644
--- a/python/ray/__init__.py
+++ b/python/ray/__init__.py
@@ -11,12 +11,19 @@ logger = logging.getLogger(__name__)
 
 if "pickle5" in sys.modules:
     import pkg_resources
-    version_info = pkg_resources.require("pickle5")
-    version = tuple(int(n) for n in version_info[0].version.split("."))
-    if version < (0, 0, 10):
-        raise ImportError("You are using an old version of pickle5 that "
-                          "leaks memory, please run 'pip install pickle5 -U' "
-                          "to upgrade")
+    try:
+        version_info = pkg_resources.require("pickle5")
+        version = tuple(int(n) for n in version_info[0].version.split("."))
+        if version < (0, 0, 10):
+            raise ImportError("You are using an old version of pickle5 "
+                              "that leaks memory, please run "
+                              "'pip install pickle5 -U' to upgrade")
+    except pkg_resources.DistributionNotFound:
+        logger.warning("You are using the 'pickle5' module, but "
+                       "the exact version is unknown (possibly carried as "
+                       "an internal component by another module). Please "
+                       "make sure you are using pickle5 >= 0.0.10 because "
+                       "previous versions may leak memory.")
 
 if "OMP_NUM_THREADS" not in os.environ:
     logger.debug("[ray] Forcing OMP_NUM_THREADS=1 to avoid performance "