diff --git a/xpcom/base/nsSystemInfo.cpp b/xpcom/base/nsSystemInfo.cpp
index 4c6e8a4ff17..5d8a0b6cfaf 100644
--- a/xpcom/base/nsSystemInfo.cpp
+++ b/xpcom/base/nsSystemInfo.cpp
@@ -181,7 +181,8 @@ nsSystemInfo::Init()
     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);