diff --git a/esphome/core/scheduler.cpp b/esphome/core/scheduler.cpp
index 4feb0811c9..e8b8332902 100644
--- a/esphome/core/scheduler.cpp
+++ b/esphome/core/scheduler.cpp
@@ -35,7 +35,9 @@ static constexpr uint32_t MAX_INTERVAL_DELAY = 5000;
 // Uses a stack buffer to avoid heap allocation
 // Uses ESPHOME_snprintf_P/ESPHOME_PSTR for ESP8266 to keep format strings in flash
 struct SchedulerNameLog {
-  char buffer[20];  // Enough for "id:4294967295" or "hash:0xFFFFFFFF" or "(null)"
+  // Sized for the widest formatted output: "self:0x" + 16 hex digits (64-bit pointer) + nul.
+  // Also covers "id:4294967295", "hash:0xFFFFFFFF", "iid:4294967295", "(null)".
+  char buffer[28];
 
   // Format a scheduler item name for logging
   // Returns pointer to formatted string (either static_name or internal buffer)
@@ -58,7 +60,8 @@ struct SchedulerNameLog {
       return buffer;
     } else {  // SELF_POINTER
       // static_name carries the void* key for SELF_POINTER (pointer-width union slot).
-      ESPHOME_snprintf_P(buffer, sizeof(buffer), ESPHOME_PSTR("self:%p"), static_name);
+      // Cast to const void* — %p requires a void* argument.
+      ESPHOME_snprintf_P(buffer, sizeof(buffer), ESPHOME_PSTR("self:%p"), static_cast<const void *>(static_name));
       return buffer;
     }
   }
@@ -301,19 +304,19 @@ bool HOT Scheduler::cancel_interval(Component *component, uint32_t id) {
 // passed through the existing static_name pointer slot. Matching is by raw pointer equality
 // (see matches_item_locked_'s SELF_POINTER branch). No Component pointer is stored, so
 // is_failed() skip and component-based log attribution don't apply.
-void HOT Scheduler::set_timeout(void *self, uint32_t timeout, std::function<void()> &&func) {
+void HOT Scheduler::set_timeout(const void *self, uint32_t timeout, std::function<void()> &&func) {
   this->set_timer_common_(nullptr, SchedulerItem::TIMEOUT, NameType::SELF_POINTER, static_cast<const char *>(self), 0,
                           timeout, std::move(func));
 }
-void HOT Scheduler::set_interval(void *self, uint32_t interval, std::function<void()> &&func) {
+void HOT Scheduler::set_interval(const void *self, uint32_t interval, std::function<void()> &&func) {
   this->set_timer_common_(nullptr, SchedulerItem::INTERVAL, NameType::SELF_POINTER, static_cast<const char *>(self), 0,
                           interval, std::move(func));
 }
-bool HOT Scheduler::cancel_timeout(void *self) {
+bool HOT Scheduler::cancel_timeout(const void *self) {
   return this->cancel_item_(nullptr, NameType::SELF_POINTER, static_cast<const char *>(self), 0,
                             SchedulerItem::TIMEOUT);
 }
-bool HOT Scheduler::cancel_interval(void *self) {
+bool HOT Scheduler::cancel_interval(const void *self) {
   return this->cancel_item_(nullptr, NameType::SELF_POINTER, static_cast<const char *>(self), 0,
                             SchedulerItem::INTERVAL);
 }
diff --git a/esphome/core/scheduler.h b/esphome/core/scheduler.h
index cb75dce38a..671665f4c0 100644
--- a/esphome/core/scheduler.h
+++ b/esphome/core/scheduler.h
@@ -168,11 +168,11 @@ class Scheduler {
    *
    * If you need either of those, use the existing `(Component *, id)` overloads.
    */
-  void set_timeout(void *self, uint32_t timeout, std::function<void()> &&func);
-  /// Self-keyed interval. See set_timeout(void *, ...) for semantics.
-  void set_interval(void *self, uint32_t interval, std::function<void()> &&func);
-  bool cancel_timeout(void *self);
-  bool cancel_interval(void *self);
+  void set_timeout(const void *self, uint32_t timeout, std::function<void()> &&func);
+  /// Self-keyed interval. See set_timeout(const void *, ...) for semantics.
+  void set_interval(const void *self, uint32_t interval, std::function<void()> &&func);
+  bool cancel_timeout(const void *self);
+  bool cancel_interval(const void *self);
 
  protected:
   struct SchedulerItem {
diff --git a/tests/integration/fixtures/scheduler_self_keyed.yaml b/tests/integration/fixtures/scheduler_self_keyed.yaml
index bee8a488b1..9a691136f3 100644
--- a/tests/integration/fixtures/scheduler_self_keyed.yaml
+++ b/tests/integration/fixtures/scheduler_self_keyed.yaml
@@ -21,8 +21,10 @@ script:
     then:
       - logger.log: "Testing self-keyed scheduler API"
       - lambda: |-
-          // Two distinct heap-allocated keys - they must not collide
-          // even though both are self-keyed and share no Component pointer.
+          // Two distinct keys backed by addresses of static markers — they
+          // must not collide even though both are self-keyed and share no
+          // Component pointer. Static storage gives them stable, unique
+          // addresses for the lifetime of the program.
           static int key_a_marker = 0;
           static int key_b_marker = 0;
           void *key_a = &key_a_marker;