diff --git a/extensions/openpower-pels/fapi_data_process.cpp b/extensions/openpower-pels/fapi_data_process.cpp
index a7cd1b4..d57c9da 100644
--- a/extensions/openpower-pels/fapi_data_process.cpp
+++ b/extensions/openpower-pels/fapi_data_process.cpp
@@ -159,7 +159,7 @@
     std::memcpy(&targetInfo.physBinPath, physBinPath.data(),
                 sizeof(targetInfo.physBinPath));
 
-    int ret = pdbg_target_traverse(NULL, pdbgCallbackToGetTgtReqAttrsVal,
+    int ret = pdbg_target_traverse(nullptr, pdbgCallbackToGetTgtReqAttrsVal,
                                    &targetInfo);
     if (ret == 0)
     {
diff --git a/extensions/openpower-pels/src.cpp b/extensions/openpower-pels/src.cpp
index cfa7155..cac9bf1 100644
--- a/extensions/openpower-pels/src.cpp
+++ b/extensions/openpower-pels/src.cpp
@@ -361,7 +361,7 @@
     auto ss = additionalData.getValue("PEL_SUBSYSTEM");
     if (ss)
     {
-        auto eventSubsystem = std::stoul(*ss, NULL, 16);
+        auto eventSubsystem = std::stoul(*ss, nullptr, 16);
         std::string subsystem =
             pv::getValue(eventSubsystem, pel_values::subsystemValues);
         if (subsystem == "invalid")
@@ -429,7 +429,7 @@
     {
         if (ccinString.size() == ccinSize)
         {
-            ccin = std::stoi(ccinString, 0, 16);
+            ccin = std::stoi(ccinString, nullptr, 16);
         }
     }
     catch (const std::exception& e)
diff --git a/extensions/openpower-pels/tools/peltool.cpp b/extensions/openpower-pels/tools/peltool.cpp
index 810223a..0e7ff8c 100644
--- a/extensions/openpower-pels/tools/peltool.cpp
+++ b/extensions/openpower-pels/tools/peltool.cpp
@@ -83,7 +83,7 @@
 
         try
         {
-            auto tmp = std::stoul(token.substr(i, 2), 0, 16);
+            auto tmp = std::stoul(token.substr(i, 2), nullptr, 16);
             bcdTime |= (static_cast<uint64_t>(tmp) << 56);
         }
         catch (const std::exception& err)
@@ -93,7 +93,7 @@
         i += 2;
         try
         {
-            auto tmp = std::stoul(token.substr(i, 2), 0, 16);
+            auto tmp = std::stoul(token.substr(i, 2), nullptr, 16);
             bcdTime |= (static_cast<uint64_t>(tmp) << 48);
         }
         catch (const std::exception& err)
@@ -103,7 +103,7 @@
         i += 2;
         try
         {
-            auto tmp = std::stoul(token.substr(i, 2), 0, 16);
+            auto tmp = std::stoul(token.substr(i, 2), nullptr, 16);
             bcdTime |= (static_cast<uint64_t>(tmp) << 40);
         }
         catch (const std::exception& err)
@@ -113,7 +113,7 @@
         i += 2;
         try
         {
-            auto tmp = std::stoul(token.substr(i, 2), 0, 16);
+            auto tmp = std::stoul(token.substr(i, 2), nullptr, 16);
             bcdTime |= (static_cast<uint64_t>(tmp) << 32);
         }
         catch (const std::exception& err)
@@ -123,7 +123,7 @@
         i += 2;
         try
         {
-            auto tmp = std::stoul(token.substr(i, 2), 0, 16);
+            auto tmp = std::stoul(token.substr(i, 2), nullptr, 16);
             bcdTime |= (tmp << 24);
         }
         catch (const std::exception& err)
@@ -133,7 +133,7 @@
         i += 2;
         try
         {
-            auto tmp = std::stoul(token.substr(i, 2), 0, 16);
+            auto tmp = std::stoul(token.substr(i, 2), nullptr, 16);
             bcdTime |= (tmp << 16);
         }
         catch (const std::exception& err)
@@ -143,7 +143,7 @@
         i += 2;
         try
         {
-            auto tmp = std::stoul(token.substr(i, 2), 0, 16);
+            auto tmp = std::stoul(token.substr(i, 2), nullptr, 16);
             bcdTime |= (tmp << 8);
         }
         catch (const std::exception& err)
@@ -153,7 +153,7 @@
         i += 2;
         try
         {
-            auto tmp = std::stoul(token.substr(i, 2), 0, 16);
+            auto tmp = std::stoul(token.substr(i, 2), nullptr, 16);
             bcdTime |= tmp;
         }
         catch (const std::exception& err)
@@ -174,7 +174,7 @@
     uint32_t num = 0;
     try
     {
-        num = std::stoul(fileName.substr(fileName.find("_") + 1), 0, 16);
+        num = std::stoul(fileName.substr(fileName.find("_") + 1), nullptr, 16);
     }
     catch (const std::exception& err)
     {
diff --git a/extensions/openpower-pels/user_header.cpp b/extensions/openpower-pels/user_header.cpp
index 1cce95c..a490da6 100644
--- a/extensions/openpower-pels/user_header.cpp
+++ b/extensions/openpower-pels/user_header.cpp
@@ -63,7 +63,7 @@
     auto ss = additionalData.getValue("PEL_SUBSYSTEM");
     if (ss)
     {
-        auto eventSubsystem = std::stoul(*ss, NULL, 16);
+        auto eventSubsystem = std::stoul(*ss, nullptr, 16);
         std::string subsystemString =
             pv::getValue(eventSubsystem, pel_values::subsystemValues);
         if (subsystemString == "invalid")