diff --git a/modules/plugin/base/src/nsPluginHostImpl.cpp b/modules/plugin/base/src/nsPluginHostImpl.cpp
index 2382441a1912..b52a5d1b4cb3 100644
--- a/modules/plugin/base/src/nsPluginHostImpl.cpp
+++ b/modules/plugin/base/src/nsPluginHostImpl.cpp
@@ -2951,7 +2951,7 @@ LoadXPCOMPlugin(nsIComponentManager* aComponentManager,
   // To figure out the filename of the plugin, we'll need to get the
   // plugin's CID, and then navigate through the XPCOM registry to
   // pull out the DLL name to which the CID is registered.
-  nsAutoString path(Concat(NS_LITERAL_STRING("software/mozilla/XPCOM/classID/"), NS_ConvertASCIItoUCS2(aCID)));
+  nsAutoString path( NS_READABLE_CAST(NS_LITERAL_STRING("software/mozilla/XPCOM/classID/")) + NS_READABLE_CAST(NS_ConvertASCIItoUCS2(aCID)) );
     // this contortion to append is a hack until I can figure out why the right |operator+| is not found
     //  on some platforms
 
diff --git a/modules/plugin/nglsrc/nsPluginHostImpl.cpp b/modules/plugin/nglsrc/nsPluginHostImpl.cpp
index 2382441a1912..b52a5d1b4cb3 100644
--- a/modules/plugin/nglsrc/nsPluginHostImpl.cpp
+++ b/modules/plugin/nglsrc/nsPluginHostImpl.cpp
@@ -2951,7 +2951,7 @@ LoadXPCOMPlugin(nsIComponentManager* aComponentManager,
   // To figure out the filename of the plugin, we'll need to get the
   // plugin's CID, and then navigate through the XPCOM registry to
   // pull out the DLL name to which the CID is registered.
-  nsAutoString path(Concat(NS_LITERAL_STRING("software/mozilla/XPCOM/classID/"), NS_ConvertASCIItoUCS2(aCID)));
+  nsAutoString path( NS_READABLE_CAST(NS_LITERAL_STRING("software/mozilla/XPCOM/classID/")) + NS_READABLE_CAST(NS_ConvertASCIItoUCS2(aCID)) );
     // this contortion to append is a hack until I can figure out why the right |operator+| is not found
     //  on some platforms