diff --git a/.changeset/tender-planes-brush.md b/.changeset/tender-planes-brush.md
new file mode 100644
index 0000000..f7f74df
--- /dev/null
+++ b/.changeset/tender-planes-brush.md
@@ -0,0 +1,5 @@
+---
+'fetch-nodeshim': patch
+---
+
+Fix `_final` on `InflateStream` calling `callback` before full flush.
diff --git a/src/encoding.ts b/src/encoding.ts
index aa3a141..8b1fc1c 100644
--- a/src/encoding.ts
+++ b/src/encoding.ts
@@ -37,10 +37,12 @@ class InflateStream extends Transform {
 
   _final(callback: TransformCallback) {
     if (this._inflate) {
+      this._inflate.once('finish', callback);
       this._inflate.end();
       this._inflate = undefined;
+    } else {
+      callback();
     }
-    callback();
   }
 }