diff --git a/_pytest/python.py b/_pytest/python.py
index 085e445be..c09fc6f36 100644
--- a/_pytest/python.py
+++ b/_pytest/python.py
@@ -1555,7 +1555,7 @@ class FixtureManager:
                     continue
                 fixturedefs = self.getfixturedefs(argname, parentid)
                 arg2fixturedefs[argname] = fixturedefs
-                if fixturedefs is not None:
+                if fixturedefs:
                     merge(fixturedefs[-1].argnames)
         return fixturenames_closure, arg2fixturedefs