diff --git a/lib/src/revset.pest b/lib/src/revset.pest
index a3a74c9b0..074a85ee2 100644
--- a/lib/src/revset.pest
+++ b/lib/src/revset.pest
@@ -48,11 +48,15 @@ infix_op = _{ union_op | intersection_op | difference_op | compat_add_op | compa
 
 function_name = @{ (ASCII_ALPHANUMERIC | "_")+ }
 function_arguments = {
-  (whitespace* ~ expression ~ whitespace* ~ ",")* ~ whitespace* ~ expression ~ whitespace*
+  whitespace* ~ expression ~ whitespace*
+  ~ ("," ~ whitespace* ~ expression ~ whitespace*)*
+  ~ ("," ~ whitespace*)?
   | whitespace*
 }
 formal_parameters = {
-  (whitespace* ~ identifier ~ whitespace* ~ ",")* ~ whitespace* ~ identifier ~ whitespace*
+  whitespace* ~ identifier ~ whitespace*
+  ~ ("," ~ whitespace* ~ identifier ~ whitespace*)*
+  ~ ("," ~ whitespace*)?
   | whitespace*
 }
 
diff --git a/lib/src/revset.rs b/lib/src/revset.rs
index 6eeb92126..ed223c7cd 100644
--- a/lib/src/revset.rs
+++ b/lib/src/revset.rs
@@ -2404,6 +2404,32 @@ mod tests {
                     .minus(&RevsetExpression::visible_heads())
             )
         );
+
+        // Trailing comma isn't allowed for empty argument
+        assert!(parse("branches(,)").is_err());
+        // Trailing comma is allowed for the last argument
+        assert!(parse("branches(a,)").is_ok());
+        assert!(parse("branches(a ,  )").is_ok());
+        assert!(parse("branches(,a)").is_err());
+        assert!(parse("branches(a,,)").is_err());
+        assert!(parse("branches(a  , , )").is_err());
+        assert!(parse("file(a,b,)").is_ok());
+        assert!(parse("file(a,,b)").is_err());
+    }
+
+    #[test]
+    fn test_parse_revset_alias_formal_parameter() {
+        let mut aliases_map = RevsetAliasesMap::new();
+        // Trailing comma isn't allowed for empty parameter
+        assert!(aliases_map.insert("f(,)", "none()").is_err());
+        // Trailing comma is allowed for the last parameter
+        assert!(aliases_map.insert("g(a,)", "none()").is_ok());
+        assert!(aliases_map.insert("h(a ,  )", "none()").is_ok());
+        assert!(aliases_map.insert("i(,a)", "none()").is_err());
+        assert!(aliases_map.insert("j(a,,)", "none()").is_err());
+        assert!(aliases_map.insert("k(a  , , )", "none()").is_err());
+        assert!(aliases_map.insert("l(a,b,)", "none()").is_ok());
+        assert!(aliases_map.insert("m(a,,b)", "none()").is_err());
     }
 
     #[test]