diff --git a/esphome/core/helpers.cpp b/esphome/core/helpers.cpp
index c79682fb41..6283f088f5 100644
--- a/esphome/core/helpers.cpp
+++ b/esphome/core/helpers.cpp
@@ -366,7 +366,9 @@ std::string value_accuracy_to_string(float value, int8_t accuracy_decimals) {
 
 std::string value_accuracy_with_uom_to_string(float value, int8_t accuracy_decimals, StringRef unit_of_measurement) {
   normalize_accuracy_decimals(value, accuracy_decimals);
-  char tmp[64];  // Increased to accommodate unit of measurement
+  // Buffer sized for float (up to ~15 chars) + space + typical UOM (usually <20 chars like "μS/cm")
+  // snprintf truncates safely if exceeded, though ESPHome UOMs are typically short
+  char tmp[64];
   if (unit_of_measurement.empty()) {
     snprintf(tmp, sizeof(tmp), "%.*f", accuracy_decimals, value);
   } else {
diff --git a/esphome/core/helpers.h b/esphome/core/helpers.h
index 51115105ac..3b38af0dd8 100644
--- a/esphome/core/helpers.h
+++ b/esphome/core/helpers.h
@@ -14,10 +14,6 @@
 
 #include "esphome/core/optional.h"
 
-namespace esphome {
-class StringRef;
-}
-
 #ifdef USE_ESP8266
 #include <Esp.h>
 #endif
@@ -49,6 +45,9 @@ class StringRef;
 
 namespace esphome {
 
+// Forward declaration to avoid circular dependency with string_ref.h
+class StringRef;
+
 /// @name STL backports
 ///@{