diff --git a/package.json b/package.json
index d5f5ded6..545c1291 100644
--- a/package.json
+++ b/package.json
@@ -42,7 +42,7 @@
     "protons": "^1.0.1",
     "rsa-pem-to-jwk": "^1.1.3",
     "tweetnacl": "^1.0.0",
-    "ursa-optional": "^0.9.8",
+    "ursa-optional": "~0.9.8",
     "webcrypto-shim": "github:dignifiedquire/webcrypto-shim#master"
   },
   "devDependencies": {