diff --git a/esphome/components/sml/sml_parser.cpp b/esphome/components/sml/sml_parser.cpp
index 85e5a2da03..16e37949dc 100644
--- a/esphome/components/sml/sml_parser.cpp
+++ b/esphome/components/sml/sml_parser.cpp
@@ -104,7 +104,10 @@ std::vector<ObisInfo> SmlFile::get_obis_info() {
 std::string bytes_repr(const BytesView &buffer) {
   std::string repr;
   for (auto const value : buffer) {
-    repr += str_sprintf("%02x", value & 0xff);
+    // max 3: 2 hex digits + null
+    char hex_buf[3];
+    snprintf(hex_buf, sizeof(hex_buf), "%02x", static_cast<unsigned int>(value));
+    repr += hex_buf;
   }
   return repr;
 }
@@ -146,7 +149,11 @@ ObisInfo::ObisInfo(const BytesView &server_id, const SmlNode &val_list_entry) :
 }
 
 std::string ObisInfo::code_repr() const {
-  return str_sprintf("%d-%d:%d.%d.%d", this->code[0], this->code[1], this->code[2], this->code[3], this->code[4]);
+  // max 20: "255-255:255.255.255" (19 chars) + null
+  char buf[20];
+  snprintf(buf, sizeof(buf), "%d-%d:%d.%d.%d", this->code[0], this->code[1], this->code[2], this->code[3],
+           this->code[4]);
+  return buf;
 }
 
 }  // namespace sml