diff --git a/crates/cli-support/src/js/mod.rs b/crates/cli-support/src/js/mod.rs
index ed80e795..65258e06 100644
--- a/crates/cli-support/src/js/mod.rs
+++ b/crates/cli-support/src/js/mod.rs
@@ -907,6 +907,7 @@ impl<'a> Context<'a> {
             return;
         }
         self.global(&format!("const heap = new Array({});", INITIAL_HEAP_OFFSET));
+        self.global("heap.fill(undefined);");
         self.global(&format!("heap.push({});", INITIAL_HEAP_VALUES.join(", ")));
     }