diff --git a/js/src/jit-test/tests/baseline/long-proto-chains.js b/js/src/jit-test/tests/baseline/long-proto-chains.js
new file mode 100644
index 000000000000..ceb387b0872f
--- /dev/null
+++ b/js/src/jit-test/tests/baseline/long-proto-chains.js
@@ -0,0 +1,10 @@
+function f() {
+    var o = {x: 1};
+    for (var i = 0; i < 300; i++)
+        o = Object.create(o);
+    for (var i = 0; i < 15; i++) {
+        assertEq(o.x, 1);
+        assertEq(o.y, undefined);
+    }
+}
+f();
diff --git a/js/src/jit/CacheIR.h b/js/src/jit/CacheIR.h
index 67a78093bfd3..446d95f988eb 100644
--- a/js/src/jit/CacheIR.h
+++ b/js/src/jit/CacheIR.h
@@ -147,8 +147,8 @@ class MOZ_RAII CacheIRWriter
     }
 
     void writeOperandId(OperandId opId) {
-        MOZ_ASSERT(size_t(opId.id()) <= UINT8_MAX);
         if (opId.id() < MaxOperandIds) {
+            static_assert(MaxOperandIds <= UINT8_MAX, "operand id must fit in a single byte");
             buffer_.writeByte(opId.id());
         } else {
             tooLarge_ = true;