diff --git a/lib/wasi-virt.js b/lib/wasi-virt.js
index a4814f0..c716119 100644
--- a/lib/wasi-virt.js
+++ b/lib/wasi-virt.js
@@ -300,6 +300,19 @@ class Descriptor {
     return new WriteStream(this.entry, offset);
   }
 
+  setSize(size) {
+    if (this.entry instanceof Directory)
+      throw 'is-directory';
+    size = Number(size);
+    if (size > this.entry.data.length) {
+      const newData = new Uint8Array(size);
+      newData.set(this.entry.data);
+      this.entry.data = newData;
+    } else if (size < this.entry.data.length) {
+      this.entry.data = this.entry.data.subarray(0, size);
+    }
+  }
+
   readDirectory() {
     return new DirectoryEntryStream(this.entry);
   }