--- a/xpcom/base/nsSystemInfo.cpp
+++ b/xpcom/base/nsSystemInfo.cpp
@@ -176,17 +176,18 @@ nsSystemInfo::Init()
       }
     }
 
 #if defined(XP_WIN) && defined(MOZ_METRO)
     // Create "hasWindowsTouchInterface" property.
     nsAutoString version;
     rv = GetPropertyAsAString(NS_LITERAL_STRING("version"), version);
     NS_ENSURE_SUCCESS(rv, rv);
-    double versionDouble = atof(NS_ConvertUTF16toUTF8(version).get());
+    double versionDouble = version.ToDouble(&rv);
+    NS_ENSURE_SUCCESS(rv, rv);
 
     rv = SetPropertyAsBool(NS_ConvertASCIItoUTF16("hasWindowsTouchInterface"),
       versionDouble >= 6.2);
     NS_ENSURE_SUCCESS(rv, rv);
 #else
     rv = SetPropertyAsBool(NS_ConvertASCIItoUTF16("hasWindowsTouchInterface"), false);
     NS_ENSURE_SUCCESS(rv, rv);
 #endif