diff --git a/lang/parser/src/cst.rs b/lang/parser/src/cst.rs
index 177f2a98d..628254335 100644
--- a/lang/parser/src/cst.rs
+++ b/lang/parser/src/cst.rs
@@ -35,6 +35,7 @@ pub enum Decl {
     Codata(Codata),
     Def(Def),
     Codef(Codef),
+    Let(Let),
 }
 
 #[derive(Debug, Clone)]
@@ -99,6 +100,17 @@ pub struct Codef {
     pub body: Match,
 }
 
+#[derive(Debug, Clone)]
+pub struct Let {
+    pub span: Span,
+    pub doc: Option<DocComment>,
+    pub name: Ident,
+    pub attr: Attribute,
+    pub params: Telescope,
+    pub typ: Rc<Exp>,
+    pub body: Rc<Exp>,
+}
+
 #[derive(Debug, Clone)]
 pub struct Match {
     pub span: Span,
diff --git a/lang/parser/src/grammar/cst.lalrpop b/lang/parser/src/grammar/cst.lalrpop
index 43c4a26d8..5557c66cb 100644
--- a/lang/parser/src/grammar/cst.lalrpop
+++ b/lang/parser/src/grammar/cst.lalrpop
@@ -22,7 +22,7 @@ match {
     r"0|[1-9][0-9]*",
     // Keywords
     "data", "codata",
-    "def", "codef",
+    "def", "codef", "let",
     "match", "as", "comatch",
     "absurd", "..absurd",
     "Type",
@@ -95,6 +95,8 @@ pub Decl: Decl = {
     <l: @L> <doc: DocComment?> <attr: OptAttribute> "codata" <name: UpperIdent> <params: OptTelescope> "{" <dtors: Comma<Dtor>> "}" <r: @R> => Decl::Codata(Codata { span: span(l, r), doc, name, attr, params, dtors }),
     <l: @L> <doc: DocComment?> <attr: OptAttribute> "def" <scrutinee: Scrutinee> "." <name: LowerIdent> <params: OptTelescope> ":" <ret_typ: Exp> "{" <body: Match> "}" <r: @R> => Decl::Def(Def { span: span(l, r), doc, name, attr, params, scrutinee, ret_typ, body }),
     <l: @L> <doc: DocComment?> <attr: OptAttribute> "codef" <name: UpperIdent> <params: OptTelescope> ":" <typ: TypApp> "{" <body: Match> "}" <r: @R> => Decl::Codef(Codef { span: span(l, r), doc, name, attr, params, typ, body }),
+    <l: @L> <doc: DocComment?> <attr: OptAttribute> "let" <name: LowerIdent><params: OptTelescope> ":" <typ: Exp> "{" <body: Exp> "}" <r: @R> =>
+    Decl::Let(Let { span: span(l,r), doc, name, attr, params, typ, body }),
 }
 
 Ctor: Ctor = {