diff --git a/js/xpconnect/loader/moz.build b/js/xpconnect/loader/moz.build
index af7d6b10a8d7..38fa13e1275d 100644
--- a/js/xpconnect/loader/moz.build
+++ b/js/xpconnect/loader/moz.build
@@ -4,6 +4,8 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
+# These files cannot be built in unified mode because they rely on plarena.h
+# and they want to force NSPR logging.
 SOURCES += [
     'mozJSComponentLoader.cpp',
     'mozJSLoaderUtils.cpp',
diff --git a/js/xpconnect/src/moz.build b/js/xpconnect/src/moz.build
index f429b521bd45..7cf3c7416ac0 100644
--- a/js/xpconnect/src/moz.build
+++ b/js/xpconnect/src/moz.build
@@ -13,13 +13,12 @@ EXPORTS += [
     'xpcpublic.h',
 ]
 
-SOURCES += [
+UNIFIED_SOURCES += [
     'nsCxPusher.cpp',
     'nsScriptError.cpp',
     'nsXPConnect.cpp',
     'Sandbox.cpp',
     'XPCCallContext.cpp',
-    'XPCComponents.cpp',
     'XPCContext.cpp',
     'XPCConvert.cpp',
     'XPCDebug.cpp',
@@ -48,6 +47,11 @@ SOURCES += [
     'XPCWrapper.cpp',
 ]
 
+# XPCComponents.cpp cannot be built in unified mode because it uses plarena.h.
+SOURCES += [
+    'XPCComponents.cpp',
+]
+
 GENERATED_SOURCES += [
     'DictionaryHelpers.cpp',
     'dom_quickstubs.cpp',
diff --git a/js/xpconnect/tests/components/native/moz.build b/js/xpconnect/tests/components/native/moz.build
index a1d17d666102..bb6c4e8040de 100644
--- a/js/xpconnect/tests/components/native/moz.build
+++ b/js/xpconnect/tests/components/native/moz.build
@@ -6,7 +6,7 @@
 
 NO_DIST_INSTALL = True
 
-SOURCES += [
+UNIFIED_SOURCES += [
     'xpctest_attributes.cpp',
     'xpctest_module.cpp',
     'xpctest_params.cpp',
diff --git a/js/xpconnect/wrappers/moz.build b/js/xpconnect/wrappers/moz.build
index a12a03ef6f97..0166a091f40c 100644
--- a/js/xpconnect/wrappers/moz.build
+++ b/js/xpconnect/wrappers/moz.build
@@ -8,12 +8,16 @@ EXPORTS += [
     'WrapperFactory.h',
 ]
 
-SOURCES += [
+UNIFIED_SOURCES += [
     'AccessCheck.cpp',
     'ChromeObjectWrapper.cpp',
     'FilteringWrapper.cpp',
     'WaiveXrayWrapper.cpp',
     'WrapperFactory.cpp',
+]
+
+# XrayWrapper needs to be built separately becaue of template instantiations.
+SOURCES += [
     'XrayWrapper.cpp',
 ]