diff --git a/CHANGELOG.md b/CHANGELOG.md
index 73ce8f94d..23bb2ff87 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ All notable changes to this project will be documented in this file.
 - Allow acl in mqtt when client certificate is in use with `#define USE_MQTT_CLIENT_CERT` (#22998)
 - Berry `tasmota.when_network_up()` and simplified Matter using it (#23057)
 - Berry `introspect.solidified()` to know if a Berry object is solidified or in RAM (#23063)
+- Berry `global.undef()` to undefine a global variable
 
 ### Breaking Changed
 
diff --git a/lib/libesp32/berry/src/be_api.c b/lib/libesp32/berry/src/be_api.c
index 6ccb65c5a..fab94ddcd 100644
--- a/lib/libesp32/berry/src/be_api.c
+++ b/lib/libesp32/berry/src/be_api.c
@@ -82,8 +82,8 @@ BERRY_API void be_regfunc(bvm *vm, const char *name, bntvfunc f)
     bstring *s = be_newstr(vm, name);
 #if !BE_USE_PRECOMPILED_OBJECT
     int idx = be_builtin_find(vm, s);
-    be_assert(idx == -1);
-    if (idx == -1) { /* new function */
+    be_assert(idx < 0);
+    if (idx < 0) { /* new function */
         idx = be_builtin_new(vm, s);
 #else
     int idx = be_global_find(vm, s);
@@ -102,8 +102,8 @@ BERRY_API void be_regclass(bvm *vm, const char *name, const bnfuncinfo *lib)
     bstring *s = be_newstr(vm, name);
 #if !BE_USE_PRECOMPILED_OBJECT
     int idx = be_builtin_find(vm, s);
-    be_assert(idx == -1);
-    if (idx == -1) { /* new function */
+    be_assert(idx < 0);
+    if (idx < 0) { /* new function */
         idx = be_builtin_new(vm, s);
 #else
     int idx = be_global_find(vm, s);
@@ -599,7 +599,7 @@ BERRY_API bbool be_getglobal(bvm *vm, const char *name)
 {
     int idx = be_global_find(vm, be_newstr(vm, name));
     bvalue *top = be_incrtop(vm);
-    if (idx > -1) {
+    if (idx >= 0) {
         *top = *be_global_var(vm, idx);
         return btrue;
     }
diff --git a/lib/libesp32/berry/src/be_globallib.c b/lib/libesp32/berry/src/be_globallib.c
index 6597fe78b..ef247a34d 100644
--- a/lib/libesp32/berry/src/be_globallib.c
+++ b/lib/libesp32/berry/src/be_globallib.c
@@ -27,10 +27,14 @@ static void dump_map_keys(bvm *vm, bmap *map)
     bmapiter iter = be_map_iter();
     while ((node = be_map_next(map, &iter)) != NULL) {
         if (var_isstr(&node->key)) {
-            bstring *s = var_tostr(&node->key);
-            be_pushstring(vm, str(s));
-            be_data_push(vm, -2);
-            be_pop(vm, 1);
+            /* check if the global was not undefined/removed */
+            int idx = var_toidx(&node->value);
+            if (idx >= 0) {     /* the key is present in global, and the index is valid */
+                bstring *s = var_tostr(&node->key);
+                be_pushstring(vm, str(s));
+                be_data_push(vm, -2);
+                be_pop(vm, 1);
+            }
         }
     }
 }
@@ -49,7 +53,7 @@ static int m_contains(bvm *vm)
     if (top >= 1 && be_isstring(vm, 1)) {
         const char * name = be_tostring(vm, 1);
         int idx = be_global_find(vm, be_newstr(vm, name));
-        be_pushbool(vm, idx > -1);
+        be_pushbool(vm, idx >= 0);
         be_return(vm);
     }
     be_return_nil(vm);
@@ -76,12 +80,25 @@ static int m_setglobal(bvm *vm)
     be_return_nil(vm);
 }
 
+/* Remove a global variable from global scope */
+/* Internally the global name cannot be removed but it's value is replaced with BE_NONE */
+/* and global function pretend that BE_NONE is equivalent to the name being absent */
+static int m_undef(bvm *vm)
+{
+    int top = be_top(vm);
+    if (top >= 1 && be_isstring(vm, 1)) {
+        be_global_undef(vm, be_newstr(vm, be_tostring(vm, 1)));
+    }
+    be_return_nil(vm);
+}
+
 #if !BE_USE_PRECOMPILED_OBJECT
 be_native_module_attr_table(global) {
     be_native_module_function("()", m_globals),
     be_native_module_function("contains", m_contains),
     be_native_module_function("member", m_findglobal),
     be_native_module_function("setmember", m_setglobal),
+    be_native_module_function("undef", m_undef),
 };
 
 be_define_native_module(global, NULL);
@@ -92,6 +109,7 @@ module global (scope: global, depend: BE_USE_GLOBAL_MODULE) {
     contains, func(m_contains)
     member, func(m_findglobal)
     setmember, func(m_setglobal)
+    undef, func(m_undef)
 }
 @const_object_info_end */
 #include "../generate/be_fixed_global.h"
diff --git a/lib/libesp32/berry/src/be_var.c b/lib/libesp32/berry/src/be_var.c
index 1a8e5b18c..c243d6747 100644
--- a/lib/libesp32/berry/src/be_var.c
+++ b/lib/libesp32/berry/src/be_var.c
@@ -67,19 +67,39 @@ static int global_find(bvm *vm, bstring *name)
 {
     bvalue *res = be_map_findstr(vm, global(vm).vtab, name);
     if (res) {
-        return var_toidx(res) + be_builtin_count(vm);
+        int idx = var_toidx(res);
+        if (idx >= 0) {
+            return idx + be_builtin_count(vm);
+        } else {
+            return idx;     /* the global does not exist (-1) or was underfined (< -1)*/
+        }
     }
     return -1; /* not found */
 }
 
+bbool be_global_undef(bvm *vm, bstring *name)
+{
+    int idx = global_find(vm, name);
+    if (idx >= 0) {
+        bvalue *desc = be_map_findstr(vm, global(vm).vtab, name);
+        int index = var_toidx(desc);
+        var_setint(desc, -index - 2);   /* negate the index to mark it as undefined */
+
+        bvalue* val = be_vector_at(&global(vm).vlist, index);
+        var_setnil(val);
+        return btrue;
+    }
+    return bfalse;
+}
+
 int be_global_find(bvm *vm, bstring *name)
 {
-    int res = global_find(vm, name);
+    int res = global_find(vm, name);                /* returns negative if not found, -1 if does not exist, < -1 if existed but undefined */
     if (res < 0) {
-        res = be_builtin_find(vm, name);
+        res = be_builtin_find(vm, name);            /* returns -1 if not found */
     }
     if (res < 0) {
-        res = global_native_class_find(vm, name);
+        res = global_native_class_find(vm, name);   /* returns -1 if not found */
     }
     return res;
 }
@@ -97,11 +117,18 @@ static int global_new_anonymous(bvm *vm)
 int be_global_new(bvm *vm, bstring *name)
 {
     int idx = global_find(vm, name);
-    if (idx == -1) {
+    if (idx < 0) {
         bvalue *desc;
-        idx = global_new_anonymous(vm);
-        desc = be_map_insertstr(vm, global(vm).vtab, name, NULL);
-        var_setint(desc, idx);
+        if (idx == -1) {
+            idx = global_new_anonymous(vm);
+            desc = be_map_insertstr(vm, global(vm).vtab, name, NULL);
+            var_setint(desc, idx);
+        } else {
+            /* the global exists but was undefined */
+            idx = -idx - 2;
+            desc = be_map_findstr(vm, global(vm).vtab, name);
+            var_setint(desc, idx);
+        }
         idx += be_builtin_count(vm);
     }
     return idx;
diff --git a/lib/libesp32/berry/src/be_var.h b/lib/libesp32/berry/src/be_var.h
index 6b9908a6b..d81623b07 100644
--- a/lib/libesp32/berry/src/be_var.h
+++ b/lib/libesp32/berry/src/be_var.h
@@ -20,6 +20,7 @@ void be_globalvar_init(bvm *vm);
 void be_globalvar_deinit(bvm *vm);
 int be_global_find(bvm *vm, bstring *name);
 int be_global_new(bvm *vm, bstring *name);
+bbool be_global_undef(bvm *vm, bstring *name);
 bvalue* be_global_var(bvm *vm, int index);
 void be_global_release_space(bvm *vm);
 int be_builtin_find(bvm *vm, bstring *name);
diff --git a/lib/libesp32/berry/src/be_vm.c b/lib/libesp32/berry/src/be_vm.c
index 78fcc486b..dcd2c7d7c 100644
--- a/lib/libesp32/berry/src/be_vm.c
+++ b/lib/libesp32/berry/src/be_vm.c
@@ -591,7 +591,7 @@ newframe: /* a new call frame */
             if (var_isstr(b)) {
                 bstring *name = var_tostr(b);
                 int idx = be_global_find(vm, name);
-                if (idx > -1) {
+                if (idx >= 0) {
                     *v = *be_global_var(vm, idx);
                 } else {
                     vm_error(vm, "attribute_error", "'%s' undeclared", str(name));