diff --git a/src/sim/syscall_emul.hh b/src/sim/syscall_emul.hh
--- a/src/sim/syscall_emul.hh
+++ b/src/sim/syscall_emul.hh
@@ -586,7 +586,7 @@
     if (startswith(path, "/dev/")) {
         std::string filename = path.substr(strlen("/dev/"));
         EmulatedDriver *drv = p->findDriver(filename);
-        if (drv != NULL) {
+        if (drv != nullptr) {
             // driver's open method will allocate a fd if necessary.
             DPRINTF_SYSCALL(Verbose, "open%s: passing call to "
                             "driver open with path[%s]\n",
@@ -1135,7 +1135,7 @@
         return -EINVAL;
 
     ThreadContext *ctc;
-    if ((ctc = p->stealFreeContext()) == NULL)
+    if ((ctc = p->stealFreeContext()) == nullptr)
         fatal("clone: no spare thread context in system");
 
     ProcessParams *pp = new ProcessParams();
@@ -1402,7 +1402,7 @@
 
         sim_fd = ffd->getSimFD();
 
-        pmap = (decltype(pmap))mmap(NULL, length, PROT_READ, MAP_PRIVATE,
+        pmap = (decltype(pmap))mmap(nullptr, length, PROT_READ, MAP_PRIVATE,
                                     sim_fd, offset);
 
         if (pmap == (decltype(pmap))-1) {
# Node ID 3b22b3ca467562233f3e469d2d55bbaa1968268a
# Parent  2b1d19988d1e821287c2a0d08691f6ebee6aeb16
diff --git a/src/sim/syscall_emul.cc b/src/sim/syscall_emul.cc
--- a/src/sim/syscall_emul.cc
+++ b/src/sim/syscall_emul.cc
@@ -425,7 +425,7 @@
         strncpy((char *)buf.bufferPtr(), cwd.c_str(), size);
         result = cwd.length();
     } else {
-        if (getcwd((char *)buf.bufferPtr(), size) != NULL) {
+        if (getcwd((char *)buf.bufferPtr(), size) != nullptr) {
             result = strlen((char *)buf.bufferPtr());
         } else {
             result = -1;
@@ -819,7 +819,7 @@
         return 0;
     }
 
-    Process *matched_ph = NULL;
+    Process *matched_ph = nullptr;
     System *sysh = tc->getSystemPtr();
 
     // Retrieves process pointer from active/suspended thread contexts.
@@ -833,7 +833,7 @@
         }
     }
 
-    assert(matched_ph != NULL);
+    assert(matched_ph != nullptr);
     matched_ph->setpgid((pgid == 0) ? matched_ph->pid() : pgid);
 
     return 0;