diff --git a/dom/base/Navigator.cpp b/dom/base/Navigator.cpp
index d1af772ba3..6509d8231f 100644
--- a/dom/base/Navigator.cpp
+++ b/dom/base/Navigator.cpp
@@ -864,37 +864,37 @@ Navigator::SendBeacon(const nsAString& aUrl,
                       ErrorResult& aRv)
 {
   if (aData.IsNull()) {
-    return SendBeaconInternal(aUrl, nullptr, /* isBlob */ false, aRv);
+    return SendBeaconInternal(aUrl, nullptr, eBeaconTypeOther, aRv);
   }
 
   if (aData.Value().IsArrayBuffer()) {
     BodyExtractor<const ArrayBuffer> body(&aData.Value().GetAsArrayBuffer());
-    return SendBeaconInternal(aUrl, &body, /* isBlob*/ false, aRv);
+    return SendBeaconInternal(aUrl, &body, eBeaconTypeOther, aRv);
   }
 
   if (aData.Value().IsArrayBufferView()) {
     BodyExtractor<const ArrayBufferView> body(&aData.Value().GetAsArrayBufferView());
-    return SendBeaconInternal(aUrl, &body, /* isBlob*/ false, aRv);
+    return SendBeaconInternal(aUrl, &body, eBeaconTypeOther, aRv);
   }
 
   if (aData.Value().IsBlob()) {
     BodyExtractor<nsIXHRSendable> body(&aData.Value().GetAsBlob());
-    return SendBeaconInternal(aUrl, &body, /* isBlob */ true, aRv);
+    return SendBeaconInternal(aUrl, &body, eBeaconTypeOther, aRv);
   }
 
   if (aData.Value().IsFormData()) {
     BodyExtractor<nsIXHRSendable> body(&aData.Value().GetAsFormData());
-    return SendBeaconInternal(aUrl, &body, /* isBlob */ false, aRv);
+    return SendBeaconInternal(aUrl, &body, eBeaconTypeOther, aRv);
   }
 
   if (aData.Value().IsUSVString()) {
     BodyExtractor<const nsAString> body(&aData.Value().GetAsUSVString());
-    return SendBeaconInternal(aUrl, &body, /* isBlob */ false, aRv);
+    return SendBeaconInternal(aUrl, &body, eBeaconTypeOther, aRv);
   }
 
   if (aData.Value().IsURLSearchParams()) {
     BodyExtractor<nsIXHRSendable> body(&aData.Value().GetAsURLSearchParams());
-    return SendBeaconInternal(aUrl, &body, /* isBlob */ false, aRv);
+    return SendBeaconInternal(aUrl, &body, eBeaconTypeOther, aRv);
   }
 
   MOZ_CRASH("Invalid data type.");
@@ -904,7 +904,7 @@ Navigator::SendBeacon(const nsAString& aUrl,
 bool
 Navigator::SendBeaconInternal(const nsAString& aUrl,
                               BodyExtractorBase* aBody,
-                              bool aIsBlob,
+                              BeaconType aType,
                               ErrorResult& aRv)
 {
   if (!mWindow) {
@@ -947,7 +947,7 @@ Navigator::SendBeaconInternal(const nsAString& aUrl,
     nsIChannel::LOAD_CLASSIFY_URI;
 
   // No need to use CORS for sendBeacon unless it's a BLOB
-  nsSecurityFlags securityFlags = aIsBlob
+  nsSecurityFlags securityFlags = aType == eBeaconTypeBlob
     ? nsILoadInfo::SEC_REQUIRE_CORS_DATA_INHERITS
     : nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_DATA_INHERITS;
   securityFlags |= nsILoadInfo::SEC_COOKIES_INCLUDE;
@@ -987,6 +987,12 @@ Navigator::SendBeaconInternal(const nsAString& aUrl,
       return false;
     }
 
+    if (aType == eBeaconTypeArrayBuffer) {
+      MOZ_ASSERT(contentTypeWithCharset.IsEmpty());
+      MOZ_ASSERT(charset.IsEmpty());
+      contentTypeWithCharset.Assign("application/octet-stream");
+    }
+
     nsCOMPtr<nsIUploadChannel2> uploadChannel = do_QueryInterface(channel);
     if (!uploadChannel) {
       aRv.Throw(NS_ERROR_FAILURE);
diff --git a/dom/base/Navigator.h b/dom/base/Navigator.h
index 16fcd4d440..f121af383c 100644
--- a/dom/base/Navigator.h
+++ b/dom/base/Navigator.h
@@ -256,9 +256,17 @@ private:
   bool CheckPermission(const char* type);
   static bool CheckPermission(nsPIDOMWindowInner* aWindow, const char* aType);
 
+  // This enum helps SendBeaconInternal to apply different behaviors to body
+  // types.
+  enum BeaconType {
+    eBeaconTypeBlob,
+    eBeaconTypeArrayBuffer,
+    eBeaconTypeOther
+  };
+
   bool SendBeaconInternal(const nsAString& aUrl,
                           BodyExtractorBase* aBody,
-                          bool aIsBlob,
+                          BeaconType aType,
                           ErrorResult& aRv);
 
   RefPtr<nsMimeTypeArray> mMimeTypes;
diff --git a/dom/tests/mochitest/beacon/beacon-handler.sjs b/dom/tests/mochitest/beacon/beacon-handler.sjs
index e4a98f7202..4c51d371d8 100644
--- a/dom/tests/mochitest/beacon/beacon-handler.sjs
+++ b/dom/tests/mochitest/beacon/beacon-handler.sjs
@@ -88,8 +88,7 @@ function handleRequest(request, response) {
       data += charcode;
     }
 
-    var mimetype = request.hasHeader("Content-Type")
-      ? request.getHeader("Content-Type") : "application/octet-stream";
+    var mimetype = request.getHeader("Content-Type");
 
     // check to see if this is form data.
     if (mimetype.indexOf("multipart/form-data") != -1) {