diff --git a/redfish-core/include/event_service_manager.hpp b/redfish-core/include/event_service_manager.hpp
index 6b3f84f..d581aeb 100644
--- a/redfish-core/include/event_service_manager.hpp
+++ b/redfish-core/include/event_service_manager.hpp
@@ -235,15 +235,17 @@
     // Get the Message from the MessageRegistry
     const registries::Message* message = registries::formatMessage(messageID);
 
-    std::string msg;
-    std::string severity;
-    if (message != nullptr)
+    if (message == nullptr)
     {
-        msg = message->message;
-        severity = message->messageSeverity;
+        return -1;
     }
 
-    redfish::registries::fillMessageArgs(messageArgs, msg);
+    std::string msg =
+        redfish::registries::fillMessageArgs(messageArgs, message->message);
+    if (msg.empty())
+    {
+        return -1;
+    }
 
     // Get the Created time from the timestamp. The log timestamp is in
     // RFC3339 format which matches the Redfish format except for the
@@ -258,7 +260,7 @@
     // Fill in the log entry with the gathered data
     logEntryJson["EventId"] = logEntryID;
     logEntryJson["EventType"] = "Event";
-    logEntryJson["Severity"] = std::move(severity);
+    logEntryJson["Severity"] = message->messageSeverity;
     logEntryJson["Message"] = std::move(msg);
     logEntryJson["MessageId"] = messageID;
     logEntryJson["MessageArgs"] = messageArgs;
diff --git a/redfish-core/include/registries.hpp b/redfish-core/include/registries.hpp
index a995d76..4247aa8 100644
--- a/redfish-core/include/registries.hpp
+++ b/redfish-core/include/registries.hpp
@@ -16,7 +16,10 @@
 #pragma once
 
 #include <array>
+#include <charconv>
 #include <cstddef>
+#include <iostream>
+#include <numeric>
 #include <span>
 #include <string>
 #include <string_view>
@@ -50,20 +53,40 @@
 };
 using MessageEntry = std::pair<const char*, const Message>;
 
-inline void fillMessageArgs(const std::span<const std::string_view> messageArgs,
-                            std::string& msg)
+inline std::string
+    fillMessageArgs(const std::span<const std::string_view> messageArgs,
+                    std::string_view msg)
 {
-    int i = 0;
-    for (const std::string_view& messageArg : messageArgs)
+    std::string ret;
+    size_t reserve = msg.size();
+    for (const std::string_view& arg : messageArgs)
     {
-        std::string argStr = "%" + std::to_string(i + 1);
-        size_t argPos = msg.find(argStr);
-        if (argPos != std::string::npos)
-        {
-            msg.replace(argPos, argStr.length(), messageArg);
-        }
-        i++;
+        reserve += arg.size();
     }
+    ret.reserve(reserve);
+
+    for (size_t stringIndex = msg.find('%'); stringIndex != std::string::npos;
+         stringIndex = msg.find('%'))
+    {
+        ret += msg.substr(0, stringIndex);
+        msg.remove_prefix(stringIndex + 1);
+        size_t number = 0;
+        auto it = std::from_chars(msg.data(), &*msg.end(), number);
+        if (it.ec != std::errc())
+        {
+            return "";
+        }
+        msg.remove_prefix(1);
+        // Redfish message args are 1 indexed.
+        number--;
+        if (number >= messageArgs.size())
+        {
+            return "";
+        }
+        ret += messageArgs[number];
+    }
+    ret += msg;
+    return ret;
 }
 
 } // namespace redfish::registries
diff --git a/redfish-core/ut/registries_test.cpp b/redfish-core/ut/registries_test.cpp
index 87b92dc..95a093e 100644
--- a/redfish-core/ut/registries_test.cpp
+++ b/redfish-core/ut/registries_test.cpp
@@ -13,17 +13,13 @@
 
 TEST(FillMessageArgs, ArgsAreFilledCorrectly)
 {
-    std::string toFill("%1");
-    fillMessageArgs({{"foo"}}, toFill);
-    EXPECT_EQ(toFill, "foo");
-
-    toFill = "";
-    fillMessageArgs({}, toFill);
-    EXPECT_EQ(toFill, "");
-
-    toFill = "%1, %2";
-    fillMessageArgs({{"foo", "bar"}}, toFill);
-    EXPECT_EQ(toFill, "foo, bar");
+    EXPECT_EQ(fillMessageArgs({{"foo"}}, "%1"), "foo");
+    EXPECT_EQ(fillMessageArgs({}, ""), "");
+    EXPECT_EQ(fillMessageArgs({{"foo", "bar"}}, "%1, %2"), "foo, bar");
+    EXPECT_EQ(fillMessageArgs({{"foo"}}, "%1 bar"), "foo bar");
+    EXPECT_EQ(fillMessageArgs({}, "%1"), "");
+    EXPECT_EQ(fillMessageArgs({}, "%"), "");
+    EXPECT_EQ(fillMessageArgs({}, "%foo"), "");
 }
 } // namespace
-} // namespace redfish::registries
\ No newline at end of file
+} // namespace redfish::registries