diff --git a/Doc/partparse.py b/Doc/partparse.py
index ea519b6..b83ad83 100644
--- a/Doc/partparse.py
+++ b/Doc/partparse.py
@@ -1509,6 +1509,7 @@
 		ingroupch = pp[i:newi]
 		del pp[i:newi]
 		length = length - (newi-i)
+		changeit(buf, ingroupch) # catch stuff inside the optional arg
 		pp.insert(i, chunk(GROUP, ch.where, ingroupch))
 		i, length = i+1, length+1
 
diff --git a/Doc/tools/partparse.py b/Doc/tools/partparse.py
index ea519b6..b83ad83 100644
--- a/Doc/tools/partparse.py
+++ b/Doc/tools/partparse.py
@@ -1509,6 +1509,7 @@
 		ingroupch = pp[i:newi]
 		del pp[i:newi]
 		length = length - (newi-i)
+		changeit(buf, ingroupch) # catch stuff inside the optional arg
 		pp.insert(i, chunk(GROUP, ch.where, ingroupch))
 		i, length = i+1, length+1