diff --git a/dom/base/nsLocation.cpp b/dom/base/nsLocation.cpp
index d69445e7f..94d87b601 100644
--- a/dom/base/nsLocation.cpp
+++ b/dom/base/nsLocation.cpp
@@ -33,6 +33,7 @@
 #include "nsCycleCollectionParticipant.h"
 #include "nsNullPrincipal.h"
 #include "ScriptSettings.h"
+#include "mozilla/unused.h"
 #include "mozilla/dom/LocationBinding.h"
 
 using namespace mozilla;
@@ -691,9 +692,16 @@ nsLocation::SetProtocol(const nsAString& aProtocol)
     return rv;
   }
 
-  rv = uri->SetScheme(NS_ConvertUTF16toUTF8(aProtocol));
+  nsAString::const_iterator start, end;
+  aProtocol.BeginReading(start);
+  aProtocol.EndReading(end);
+  nsAstring::const_iterator iter(start);
+  Unused << FindCharInReadable(':', iter, end);
+  rv = uri->SetScheme(NS_ConvertUTF16toUTF8(Substring(start, iter)));
   if (NS_WARN_IF(NS_FAILED(rv))) {
-    return rv;
+    // Oh, I wish nsStandardURL returned NS_ERROR_MALFORMED_URI for _all_ the
+    // malformed cases, not just some of them!
+    return NS_ERROR_DOM_SYNTAX_ERR;
   }
   nsAutoCString newSpec;
   rv = uri->GetSpec(newSpec);
@@ -703,9 +711,29 @@ nsLocation::SetProtocol(const nsAString& aProtocol)
   // We may want a new URI class for the new URI, so recreate it:
   rv = NS_NewURI(getter_AddRefs(uri), newSpec);
   if (NS_FAILED(rv)) {
+    if (rv == NS_ERROR_MALFORMED_URI) {
+      rv = NS_ERROR_DOM_SYNTAX_ERR;
+    }
     return rv;
   }
 
+  bool isHttp;
+  rv = uri->SchemeIs("http", &isHttp);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  bool isHttps;
+  rv = uri->SchemeIs("https", &isHttps);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (!isHttp && !isHttps) {
+    // No-op, per spec.
+    return NS_OK;
+  }
+
   return SetURI(uri);
 }