diff --git a/feature/asi.js b/feature/asi.js
index 299b58b..26329d1 100644
--- a/feature/asi.js
+++ b/feature/asi.js
@@ -27,10 +27,16 @@ const MAX_ASI_DEPTH = 100;
 
 parse.asi = (a, p, expr, b, items) => {
   if (p >= lvl || asiDepth >= MAX_ASI_DEPTH) return;
+  // Bail if the inner expr didn't actually consume anything. Without this, a
+  // lookup handler that returns a non-array sentinel (e.g. switch.js's
+  // `reserve` flagging `case`/`default` inside a switch body) lets expr return
+  // a truthy token without advancing idx, and the outer ASI loop appends to its
+  // semicolon-list forever.
+  const beforeIdx = idx;
   asiDepth++;
   try { b = expr(lvl - .5); }
   finally { asiDepth--; }
-  if (!b) return;
+  if (!b || idx === beforeIdx) return;
   items = b?.[0] === ';' ? b.slice(1) : [b];
   return a?.[0] === ';' ? (a.push(...items), a) : [';', a, ...items];
 };
diff --git a/test/feature/control.js b/test/feature/control.js
index f871a39..aac9997 100644
--- a/test/feature/control.js
+++ b/test/feature/control.js
@@ -155,6 +155,21 @@ test('control: switch basic', t => {
   is(ast[3][0], 'case')
 })
 
+// ASI inside a switch body: when an inner expr() call hits a reserved
+// keyword that signals "matched but did not consume" (e.g. case/default
+// while inSwitch), the ASI loop must stop. Without the no-progress guard,
+// the recursion appended to its semicolon-list until the array exceeded
+// its max length and threw `Invalid array length`.
+test('control: switch with multi-statement case bodies parses without ASI loop', t => {
+  is(parse(`switch (x) {
+    case 1:
+      a
+      b
+    case 2:
+      c
+  }`)[0], 'switch')
+})
+
 test('control: switch compile', t => {
   // Basic case match
   let ctx = { x: 1, y: 0 }