diff --git a/lib/src/compiler/tests/testdata/errors/137.in b/lib/src/compiler/tests/testdata/errors/137.in
new file mode 100644
index 00000000..5fa723c5
--- /dev/null
+++ b/lib/src/compiler/tests/testdata/errors/137.in
@@ -0,0 +1,4 @@
+rule test {
+  condition:
+     uint16(,0) == 0
+}
\ No newline at end of file
diff --git a/lib/src/compiler/tests/testdata/errors/137.out b/lib/src/compiler/tests/testdata/errors/137.out
new file mode 100644
index 00000000..66ed65e4
--- /dev/null
+++ b/lib/src/compiler/tests/testdata/errors/137.out
@@ -0,0 +1,6 @@
+error[E001]: syntax error
+ --> line:3:13
+  |
+3 |      uint16(,0) == 0
+  |             ^ expecting expression, `for`, `all`, `none`, `any`, `with` or `)`, found `,`
+  |
\ No newline at end of file
diff --git a/parser/src/ast/cst2ast.rs b/parser/src/ast/cst2ast.rs
index d00aef31..2e3a321c 100644
--- a/parser/src/ast/cst2ast.rs
+++ b/parser/src/ast/cst2ast.rs
@@ -225,6 +225,10 @@ impl<'src> Builder<'src> {
         match self.next()? {
             Event::Token { kind, span } => {
                 if expected_kind != kind {
+                    // If this ever happens is because we are finding an
+                    // unexpected syntax in the CST. Either the source -> CST
+                    // phase is not strict enough, or the CST -> AST phase is
+                    // overly strict.
                     panic!("expected {:?}, got {:?}", expected_kind, kind);
                 }
                 Ok(span)
diff --git a/parser/src/parser/mod.rs b/parser/src/parser/mod.rs
index e3893f8d..b88a2205 100644
--- a/parser/src/parser/mod.rs
+++ b/parser/src/parser/mod.rs
@@ -1432,11 +1432,12 @@ impl<'src> ParserImpl<'src> {
             .then(|p| p.primary_expr())
             .cond(t!(L_BRACKET), |p| p.expr().expect(t!(R_BRACKET)))
             .cond(t!(L_PAREN), |p| {
-                p.opt(|p| p.boolean_expr())
-                    .zero_or_more(|p| {
+                p.opt(|p| {
+                    p.boolean_expr().zero_or_more(|p| {
                         p.expect(t!(COMMA)).then(|p| p.boolean_expr())
                     })
-                    .expect(t!(R_PAREN))
+                })
+                .expect(t!(R_PAREN))
             })
             .end()
     }