diff --git a/argument.cpp b/argument.cpp
index 38d3978..35f33e3 100644
--- a/argument.cpp
+++ b/argument.cpp
@@ -29,7 +29,8 @@
 ArgumentParser::ArgumentParser(int argc, char** argv)
 {
     auto option = 0;
-    while (-1 != (option = getopt_long(argc, argv, optionstr, options, NULL)))
+    while (-1 !=
+           (option = getopt_long(argc, argv, optionstr, options, nullptr)))
     {
         if ((option == '?') || (option == 'h'))
         {
diff --git a/certificate.cpp b/certificate.cpp
index 0e19141..88ff65e 100644
--- a/certificate.cpp
+++ b/certificate.cpp
@@ -90,8 +90,8 @@
 std::string
     Certificate::generateUniqueFilePath(const std::string& directoryPath)
 {
-    char* filePath = tempnam(directoryPath.c_str(), NULL);
-    if (filePath == NULL)
+    char* filePath = tempnam(directoryPath.c_str(), nullptr);
+    if (filePath == nullptr)
     {
         log<level::ERR>(
             "Error occurred while creating random certificate file path",
@@ -293,8 +293,8 @@
         elog<InternalFailure>();
     }
 
-    errCode =
-        X509_STORE_CTX_init(storeCtx.get(), x509Store.get(), cert.get(), NULL);
+    errCode = X509_STORE_CTX_init(storeCtx.get(), x509Store.get(), cert.get(),
+                                  nullptr);
     if (errCode != 1)
     {
         log<level::ERR>("Error occurred during X509_STORE_CTX_init call",
@@ -526,7 +526,7 @@
     // Go through each usage in the bit string and convert to
     // corresponding string value
     if ((usage = static_cast<ASN1_BIT_STRING*>(
-             X509_get_ext_d2i(cert.get(), NID_key_usage, NULL, NULL))))
+             X509_get_ext_d2i(cert.get(), NID_key_usage, nullptr, nullptr))))
     {
         for (auto i = 0; i < usage->length; ++i)
         {
@@ -542,8 +542,8 @@
     }
 
     EXTENDED_KEY_USAGE* extUsage;
-    if ((extUsage = static_cast<EXTENDED_KEY_USAGE*>(
-             X509_get_ext_d2i(cert.get(), NID_ext_key_usage, NULL, NULL))))
+    if ((extUsage = static_cast<EXTENDED_KEY_USAGE*>(X509_get_ext_d2i(
+             cert.get(), NID_ext_key_usage, nullptr, nullptr))))
     {
         for (int i = 0; i < sk_ASN1_OBJECT_num(extUsage); i++)
         {
diff --git a/certs_manager.cpp b/certs_manager.cpp
index 0303c9a..6aca6af 100644
--- a/certs_manager.cpp
+++ b/certs_manager.cpp
@@ -306,7 +306,7 @@
             }
 
             // Block SIGCHLD first, so that the event loop can handle it
-            if (sigprocmask(SIG_BLOCK, &ss, NULL) < 0)
+            if (sigprocmask(SIG_BLOCK, &ss, nullptr) < 0)
             {
                 log<level::ERR>("Unable to block signal");
                 elog<InternalFailure>();
@@ -470,7 +470,7 @@
     }
 
     RSA* rsa = RSA_new();
-    ret = RSA_generate_key_ex(rsa, keyBitLen, bne.get(), NULL);
+    ret = RSA_generate_key_ex(rsa, keyBitLen, bne.get(), nullptr);
     if (ret != 1)
     {
         free(rsa);
@@ -546,7 +546,7 @@
 
     EC_KEY* ecKey = EC_KEY_new_by_curve_name(ecGrp);
 
-    if (ecKey == NULL)
+    if (ecKey == nullptr)
     {
         log<level::ERR>(
             "Error occurred during create the EC_Key object from NID",
@@ -638,12 +638,13 @@
     fs::path privKeyPath = certParentInstallPath / privKeyFileName;
 
     FILE* fp = std::fopen(privKeyPath.c_str(), "w");
-    if (fp == NULL)
+    if (fp == nullptr)
     {
         log<level::ERR>("Error occurred creating private key file");
         elog<InternalFailure>();
     }
-    int ret = PEM_write_PrivateKey(fp, pKey.get(), NULL, NULL, 0, 0, NULL);
+    int ret =
+        PEM_write_PrivateKey(fp, pKey.get(), nullptr, nullptr, 0, 0, nullptr);
     std::fclose(fp);
     if (ret == 0)
     {
@@ -695,9 +696,9 @@
         }
     }
 
-    FILE* fp = NULL;
+    FILE* fp = nullptr;
 
-    if ((fp = std::fopen(filePath.c_str(), "w")) == NULL)
+    if ((fp = std::fopen(filePath.c_str(), "w")) == nullptr)
     {
         log<level::ERR>("Error opening the file to write the CSR",
                         entry("FILENAME=%s", filePath.c_str()));
diff --git a/csr.cpp b/csr.cpp
index c93a487..cf74f53 100644
--- a/csr.cpp
+++ b/csr.cpp
@@ -49,11 +49,11 @@
     }
 
     FILE* fp = std::fopen(csrFilePath.c_str(), "r");
-    X509_REQ_Ptr x509Req(PEM_read_X509_REQ(fp, NULL, NULL, NULL),
+    X509_REQ_Ptr x509Req(PEM_read_X509_REQ(fp, nullptr, nullptr, nullptr),
                          ::X509_REQ_free);
-    if (x509Req == NULL || fp == NULL)
+    if (x509Req == nullptr || fp == nullptr)
     {
-        if (fp != NULL)
+        if (fp != nullptr)
         {
             std::fclose(fp);
         }
@@ -71,7 +71,7 @@
         elog<InternalFailure>();
     }
 
-    BUF_MEM* mem = NULL;
+    BUF_MEM* mem = nullptr;
     BIO_get_mem_ptr(bio.get(), &mem);
     std::string pem(mem->data, mem->length);
     return pem;
diff --git a/test/certs_manager_test.cpp b/test/certs_manager_test.cpp
index c0c712c..38c563a 100644
--- a/test/certs_manager_test.cpp
+++ b/test/certs_manager_test.cpp
@@ -40,7 +40,7 @@
     {
         char dirTemplate[] = "/tmp/FakeCerts.XXXXXX";
         auto dirPtr = mkdtemp(dirTemplate);
-        if (dirPtr == NULL)
+        if (dirPtr == nullptr)
         {
             throw std::bad_alloc();
         }
@@ -791,7 +791,7 @@
     {
         char dirTemplate[] = "/tmp/FakeCerts.XXXXXX";
         auto dirPtr = mkdtemp(dirTemplate);
-        if (dirPtr == NULL)
+        if (dirPtr == nullptr)
         {
             throw std::bad_alloc();
         }