diff --git a/Lib/idlelib/autocomplete.py b/Lib/idlelib/autocomplete.py
index 032d31225315fb..c95c9f1a322127 100644
--- a/Lib/idlelib/autocomplete.py
+++ b/Lib/idlelib/autocomplete.py
@@ -37,8 +37,10 @@
 
 class AutoComplete:
 
-    def __init__(self, editwin=None, tags=None):
+    def __init__(self, editwin=None, tags=None, namespace=None):
+
         self.editwin = editwin
+        self.namespace = namespace
         if editwin is not None:   # not in subprocess or no-gui test
             self.text = editwin.text
         self.tags = tags
@@ -217,8 +219,17 @@ def fetch_completions(self, what, mode):
             return smalll, bigl
 
     def get_entity(self, name):
-        "Lookup name in a namespace spanning sys.modules and __main.dict__."
-        return eval(name, {**sys.modules, **__main__.__dict__})
+        """Evaluate an expression in a the execution namespace."""
+        namespace = self.namespace
+        if namespace is None:
+            try:
+                # Fallback when running without a subprocess.
+                namespace = self.editwin.flist.pyshell.interp.locals
+            except AttributeError:
+                # Fallback when there isn't a running shell.
+                namespace = {**sys.modules, **__main__.__dict__}
+
+        return eval(name, namespace)
 
 
 AutoComplete.reload()
diff --git a/Lib/idlelib/run.py b/Lib/idlelib/run.py
index 577c49eb67b20d..edd28b4e1985b1 100644
--- a/Lib/idlelib/run.py
+++ b/Lib/idlelib/run.py
@@ -565,7 +565,7 @@ def __init__(self, rpchandler):
         if idlelib.testing is False:
             self.locals = __main__.__dict__
             self.calltip = calltip.Calltip()
-            self.autocomplete = autocomplete.AutoComplete()
+            self.autocomplete = autocomplete.AutoComplete(namespace=self.locals)
         else:
             self.locals = {}
 
diff --git a/Misc/NEWS.d/next/IDLE/2019-08-11-14-20-28.bpo-37821.OVbIt_.rst b/Misc/NEWS.d/next/IDLE/2019-08-11-14-20-28.bpo-37821.OVbIt_.rst
new file mode 100644
index 00000000000000..87e05eac64d7dd
--- /dev/null
+++ b/Misc/NEWS.d/next/IDLE/2019-08-11-14-20-28.bpo-37821.OVbIt_.rst
@@ -0,0 +1,2 @@
+Fix the namespace used for completions to be that of the running shell, when
+a shell window exists.