diff --git a/lib/src/revset.pest b/lib/src/revset.pest
index 074a85ee2..810e1945c 100644
--- a/lib/src/revset.pest
+++ b/lib/src/revset.pest
@@ -48,21 +48,17 @@ 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*)?
-  | whitespace*
+  expression ~ (whitespace* ~ "," ~ whitespace* ~ expression)* ~ (whitespace* ~ ",")?
+  | ""
 }
 formal_parameters = {
-  whitespace* ~ identifier ~ whitespace*
-  ~ ("," ~ whitespace* ~ identifier ~ whitespace*)*
-  ~ ("," ~ whitespace*)?
-  | whitespace*
+  identifier ~ (whitespace* ~ "," ~ whitespace* ~ identifier)* ~ (whitespace* ~ ",")?
+  | ""
 }
 
 primary = {
-  function_name ~ "(" ~ function_arguments ~ ")"
-  | "(" ~ expression ~ ")"
+  function_name ~ "(" ~ whitespace* ~ function_arguments ~ whitespace* ~ ")"
+  | "(" ~ whitespace* ~ expression ~ whitespace* ~ ")"
   | symbol
 }
 
@@ -76,14 +72,14 @@ range_expression = _{
 }
 
 expression = {
-  whitespace* ~ (negate_op ~ whitespace*)* ~ range_expression ~ whitespace*
-  ~ (infix_op ~ whitespace* ~ (negate_op ~ whitespace*)* ~ range_expression ~ whitespace*)*
+  (negate_op ~ whitespace*)* ~ range_expression
+  ~ (whitespace* ~ infix_op ~ whitespace* ~ (negate_op ~ whitespace*)* ~ range_expression)*
 }
 
-program = _{ SOI ~ expression ~ EOI }
+program = _{ SOI ~ whitespace* ~ expression ~ whitespace* ~ EOI }
 
 alias_declaration_part = _{
-  function_name ~ "(" ~ formal_parameters ~ ")"
+  function_name ~ "(" ~ whitespace* ~ formal_parameters ~ whitespace* ~ ")"
   | identifier
 }
 alias_declaration = _{
diff --git a/lib/src/revset.rs b/lib/src/revset.rs
index 6d6e56c9a..dc02ce52c 100644
--- a/lib/src/revset.rs
+++ b/lib/src/revset.rs
@@ -2367,6 +2367,7 @@ mod tests {
         assert_eq!(parse("(@)-"), Ok(wc_symbol.parents()));
         // Space is allowed around expressions
         assert_eq!(parse(" :@ "), Ok(wc_symbol.ancestors()));
+        assert_eq!(parse("( :@ )"), Ok(wc_symbol.ancestors()));
         // Space is not allowed around prefix operators
         assert_eq!(parse(" : @ "), Err(RevsetParseErrorKind::SyntaxError));
         // Incomplete parse