diff --git a/dom/crypto/WebCryptoTask.cpp b/dom/crypto/WebCryptoTask.cpp
index 57fb3c3c86..122afd793b 100644
--- a/dom/crypto/WebCryptoTask.cpp
+++ b/dom/crypto/WebCryptoTask.cpp
@@ -690,6 +690,7 @@ private:
       case CKM_AES_GCM:
         gcmParams.pIv = mIv.Elements();
         gcmParams.ulIvLen = mIv.Length();
+        gcmParams.ulIvBits = gcmParams.ulIvLen * 8;
         gcmParams.pAAD = mAad.Elements();
         gcmParams.ulAADLen = mAad.Length();
         gcmParams.ulTagBits = mTagLength;