diff --git a/cmd/markdown/main.go b/cmd/markdown/main.go
index f9c4b68..dc2b18b 100644
--- a/cmd/markdown/main.go
+++ b/cmd/markdown/main.go
@@ -15,6 +15,7 @@ func main() {
 	var opt markdown.Extensions
 	flag.BoolVar(&opt.Notes, "notes", false, "turn on footnote syntax")
 	flag.BoolVar(&opt.Smart, "smart", false, "turn on smart quotes, dashes, and ellipses")
+	flag.BoolVar(&opt.Strike, "strike", false, "turn on strike-through syntax")
 	flag.BoolVar(&opt.Dlists, "dlists", false, "support definitions lists")
 
 	flag.Usage = func() {
diff --git a/markdown.go b/markdown.go
index a93222c..f639495 100644
--- a/markdown.go
+++ b/markdown.go
@@ -40,6 +40,7 @@ type Extensions struct {
 	Notes        bool
 	FilterHTML   bool
 	FilterStyles bool
+	Strike       bool
 	Dlists       bool
 }
 
diff --git a/parser.leg b/parser.leg
index 1246a5a..fc8b6b1 100644
--- a/parser.leg
+++ b/parser.leg
@@ -570,10 +570,11 @@ StrongUl   =    "__" !Whitespace
                 "__"
                 { $$ = p.mkList(STRONG, a) }
 
-TwoTildeOpen =  !TildeLine "~~" !Spacechar !Newline
-TwoTildeClose = !Spacechar !Newline a:Inline "~~" { $$ = a; }
+TwoTildeOpen =  &{ p.extension.Strike } !TildeLine "~~" !Spacechar !Newline
+TwoTildeClose = &{ p.extension.Strike } !Spacechar !Newline a:Inline "~~" { $$ = a; }
 
-Strike = TwoTildeOpen
+Strike = &{ p.extension.Strike }
+         TwoTildeOpen
          a:StartList
          ( !TwoTildeClose Inline { a = cons($$, a) } )*
          TwoTildeClose { a = cons($$, a) }
diff --git a/portid b/portid
index 259119c..6772f05 100644
--- a/portid
+++ b/portid
@@ -1 +1 @@
-9629df92a0de
+a79c71ede83f