diff --git a/.github/workflows/code_checks.yml b/.github/workflows/code_checks.yml
index 065271f877..d3ce8b644c 100644
--- a/.github/workflows/code_checks.yml
+++ b/.github/workflows/code_checks.yml
@@ -87,8 +87,8 @@ jobs:
         run: |
             git fetch --depth=1 origin master
             if git diff origin/master \
-               ':!.github/workflows/code_checks.yml' \
-               | grep -E '^\+.*(wxOVERRIDE|wxNOEXCEPT|[^_@]NULL)'; then
+               ':**.h' ':**.cpp' \
+               | grep -E '^\+.*(wxOVERRIDE|wxNOEXCEPT|[^"_@]NULL[^"_])'; then
               echo "::error ::Please use C++11 equivalents of the deprecated macros in the new code."
               exit 1
             fi
diff --git a/include/wx/weakref.h b/include/wx/weakref.h
index d8e16358c4..754b804400 100644
--- a/include/wx/weakref.h
+++ b/include/wx/weakref.h
@@ -31,11 +31,11 @@ public:
     typedef T element_type;
 
     // Default ctor
-    wxWeakRef() : m_pobj(nullptr), m_ptbase(nullptr) { }
+    wxWeakRef() = default;
 
     // Ctor from the object of this type: this is needed as the template ctor
     // below is not used by at least g++4 when a literal NULL is used
-    wxWeakRef(T *pobj) : m_pobj(nullptr), m_ptbase(nullptr)
+    wxWeakRef(T *pobj)
     {
         this->Assign(pobj);
     }
@@ -43,14 +43,14 @@ public:
     // When we have the full type here, static_cast<> will always work
     // (or give a straight compiler error).
     template <class TDerived>
-    wxWeakRef(TDerived* pobj) : m_pobj(nullptr), m_ptbase(nullptr)
+    wxWeakRef(TDerived* pobj)
     {
         this->Assign(pobj);
     }
 
     // We need this copy ctor, since otherwise a default compiler (binary) copy
     // happens (if embedded as an object member).
-    wxWeakRef(const wxWeakRef<T>& wr) : m_pobj(nullptr), m_ptbase(nullptr)
+    wxWeakRef(const wxWeakRef<T>& wr)
     {
         this->Assign(wr.get());
     }
@@ -124,8 +124,8 @@ protected:
         }
     }
 
-    T *m_pobj;
-    wxTrackable *m_ptbase;
+    T *m_pobj = nullptr;
+    wxTrackable *m_ptbase = nullptr;
 };
 
 
@@ -137,7 +137,7 @@ template <class T>
 class wxWeakRefDynamic : public wxTrackerNode
 {
 public:
-    wxWeakRefDynamic() : m_pobj(nullptr) { }
+    wxWeakRefDynamic() = default;
 
     wxWeakRefDynamic(T* pobj) : m_pobj(pobj)
     {
@@ -209,7 +209,7 @@ protected:
         }
     }
 
-    T *m_pobj;
+    T *m_pobj = nullptr;
 };
 
 #endif // RTTI enabled
diff --git a/samples/minimal/minimal.cpp b/samples/minimal/minimal.cpp
index 501caf9096..5f32257c6b 100644
--- a/samples/minimal/minimal.cpp
+++ b/samples/minimal/minimal.cpp
@@ -139,7 +139,7 @@ bool MyApp::OnInit()
 
 // frame constructor
 MyFrame::MyFrame(const wxString& title)
-       : wxFrame(NULL, wxID_ANY, title)
+       : wxFrame(nullptr, wxID_ANY, title)
 {
     // set the frame icon
     SetIcon(wxICON(sample));
diff --git a/src/unix/stackwalk.cpp b/src/unix/stackwalk.cpp
index 95a0dfdd59..99dac840cb 100644
--- a/src/unix/stackwalk.cpp
+++ b/src/unix/stackwalk.cpp
@@ -308,7 +308,7 @@ struct ModuleInfo
     {
     }
 
-    // Name of the file containing this address, may be NULL.
+    // Name of the file containing this address, may be null.
     const char* name;
 
     // Difference between the address in the file and in memory.
@@ -322,7 +322,7 @@ ModuleInfo GetModuleInfoFromAddr(void* addr)
     if ( !dladdr1(addr, &info, (void**)&lm, RTLD_DL_LINKMAP) )
     {
         // Probably not worth spamming the user with even debug errors.
-        return ModuleInfo(NULL, 0);
+        return ModuleInfo(nullptr, 0);
     }
 
     return ModuleInfo(info.dli_fname, lm->l_addr);
diff --git a/utils/wxrc/wxrc.cpp b/utils/wxrc/wxrc.cpp
index 137e6978eb..9c9e6ad72c 100644
--- a/utils/wxrc/wxrc.cpp
+++ b/utils/wxrc/wxrc.cpp
@@ -171,7 +171,7 @@ public:
                     m_className +
                     wxT("(") +
                         *m_ancestorClassNames.begin() +
-                        wxT(" *parent=NULL){\n") +
+                        wxT(" *parent=nullptr){\n") +
                     wxT("  InitWidgetsFromXRC((wxWindow *)parent);\n")
                     wxT(" }\n")
                     wxT("};\n")
@@ -180,7 +180,7 @@ public:
         else
         {
             file.Write(m_className + wxT("(){\n") +
-                       wxT("  InitWidgetsFromXRC(NULL);\n")
+                       wxT("  InitWidgetsFromXRC(nullptr);\n")
                        wxT(" }\n")
                        wxT("};\n"));