diff --git a/Lib/inspect.py b/Lib/inspect.py
index bb46ea6..4e17f1b 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -483,7 +483,7 @@
         return sys.modules.get(modulesbyfile[file])
     # Update the filename to module name cache and check yet again
     # Copy sys.modules in order to cope with changes while iterating
-    for modname, module in sys.modules.items():
+    for modname, module in list(sys.modules.items()):
         if ismodule(module) and hasattr(module, '__file__'):
             f = module.__file__
             if f == _filesbymodname.get(modname, None):
diff --git a/Misc/ACKS b/Misc/ACKS
index 5d75404..4effde3 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -905,6 +905,7 @@
 Frank J. Tobin
 R Lindsay Todd
 Bennett Todd
+Erik Tollerud
 Matias Torchinsky
 Sandro Tosi
 Richard Townsend
diff --git a/Misc/NEWS b/Misc/NEWS
index f79e57a..2172853 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -87,6 +87,9 @@
 Library
 -------
 
+- Issue #13487: Make inspect.getmodule robust against changes done to
+  sys.modules while it is iterating over it.
+
 - Issue #12618: Fix a bug that prevented py_compile from creating byte
   compiled files in the current directory.  Initial patch by Sjoerd de Vries.