diff --git a/Lib/idlelib/PyShell.py b/Lib/idlelib/PyShell.py
index d8a5cd24331..cde389ad009 100644
--- a/Lib/idlelib/PyShell.py
+++ b/Lib/idlelib/PyShell.py
@@ -61,7 +61,6 @@ else:
                                               lineno, line=line))
         except OSError:
             pass  ## file (probably __stderr__) is invalid, warning dropped.
-    warnings.showwarning = idle_showwarning
     def idle_formatwarning(message, category, filename, lineno, line=None):
         """Format warnings the IDLE way"""
         s = "\nWarning (from warnings module):\n"
@@ -73,7 +72,6 @@ else:
             s += "    %s\n" % line
         s += "%s: %s\n>>> " % (category.__name__, message)
         return s
-    warnings.formatwarning = idle_formatwarning
 
 def extended_linecache_checkcache(filename=None,
                                   orig_checkcache=linecache.checkcache):
@@ -1425,6 +1423,9 @@ echo "import sys; print(sys.argv)" | idle - "foobar"
 def main():
     global flist, root, use_subprocess
 
+    warnings.showwarning = idle_showwarning
+    warnings.formatwarning = idle_formatwarning
+
     use_subprocess = True
     enable_shell = False
     enable_edit = False
diff --git a/Lib/idlelib/run.py b/Lib/idlelib/run.py
index 15f44720dd7..74c1b8947a0 100644
--- a/Lib/idlelib/run.py
+++ b/Lib/idlelib/run.py
@@ -40,7 +40,6 @@ else:
             s += "    %s\n" % line
         s += "%s: %s\n" % (category.__name__, message)
         return s
-    warnings.formatwarning = idle_formatwarning_subproc
 
 
 tcl = tkinter.Tcl()
@@ -82,6 +81,9 @@ def main(del_exitfunc=False):
     global exit_now
     global quitting
     global no_exitfunc
+
+    warnings.formatwarning = idle_formatwarning_subproc
+
     no_exitfunc = del_exitfunc
     #time.sleep(15) # test subprocess not responding
     try: