diff --git a/include/osmium/builder/builder.hpp b/include/osmium/builder/builder.hpp
index 107f4a9d0..d4358843b 100644
--- a/include/osmium/builder/builder.hpp
+++ b/include/osmium/builder/builder.hpp
@@ -167,6 +167,20 @@ namespace osmium {
                 return length;
             }
 
+            /**
+             * Append data to buffer and append an additional \0.
+             *
+             * @param data Pointer to data.
+             * @param length Length of data in bytes.
+             * @returns The number of bytes appended (length + 1).
+             */
+            osmium::memory::item_size_type append_with_zero(const char* data, const osmium::memory::item_size_type length) {
+                unsigned char* target = reserve_space(length + 1);
+                std::copy_n(reinterpret_cast<const unsigned char*>(data), length, target);
+                target[length] = '\0';
+                return length + 1;
+            }
+
             /**
              * Append \0-terminated string to buffer.
              *
@@ -180,9 +194,11 @@ namespace osmium {
             /**
              * Append '\0' to the buffer.
              *
+             * @deprecated Use append_with_zero() instead.
+             *
              * @returns The number of bytes appended (always 1).
              */
-            osmium::memory::item_size_type append_zero() {
+            OSMIUM_DEPRECATED osmium::memory::item_size_type append_zero() {
                 *reserve_space(1) = '\0';
                 return 1;
             }
diff --git a/include/osmium/builder/osm_object_builder.hpp b/include/osmium/builder/osm_object_builder.hpp
index 1dd5f972f..d4483b192 100644
--- a/include/osmium/builder/osm_object_builder.hpp
+++ b/include/osmium/builder/osm_object_builder.hpp
@@ -99,7 +99,8 @@ namespace osmium {
                 if (std::strlen(value) > osmium::max_osm_string_length) {
                     throw std::length_error("OSM tag value is too long");
                 }
-                add_size(append(key) + append(value));
+                add_size(append(key));
+                add_size(append(value));
             }
 
             /**
@@ -117,8 +118,8 @@ namespace osmium {
                 if (value_length > osmium::max_osm_string_length) {
                     throw std::length_error("OSM tag value is too long");
                 }
-                add_size(append(key,   osmium::memory::item_size_type(key_length))   + append_zero() +
-                         append(value, osmium::memory::item_size_type(value_length)) + append_zero());
+                add_size(append_with_zero(key,   osmium::memory::item_size_type(key_length)));
+                add_size(append_with_zero(value, osmium::memory::item_size_type(value_length)));
             }
 
             /**
@@ -134,8 +135,8 @@ namespace osmium {
                 if (value.size() > osmium::max_osm_string_length) {
                     throw std::length_error("OSM tag value is too long");
                 }
-                add_size(append(key.data(),   osmium::memory::item_size_type(key.size())   + 1) +
-                         append(value.data(), osmium::memory::item_size_type(value.size()) + 1));
+                add_size(append(key.data(),   osmium::memory::item_size_type(key.size())   + 1));
+                add_size(append(value.data(), osmium::memory::item_size_type(value.size()) + 1));
             }
 
             /**
@@ -144,7 +145,8 @@ namespace osmium {
              * @param tag Tag.
              */
             void add_tag(const osmium::Tag& tag) {
-                add_size(append(tag.key()) + append(tag.value()));
+                add_size(append(tag.key()));
+                add_size(append(tag.value()));
             }
 
             /**
@@ -226,7 +228,7 @@ namespace osmium {
                     throw std::length_error("OSM relation member role is too long");
                 }
                 member.set_role_size(osmium::string_size_type(length) + 1);
-                add_size(append(role, osmium::memory::item_size_type(length)) + append_zero());
+                add_size(append_with_zero(role, osmium::memory::item_size_type(length)));
                 add_padding(true);
             }
 
@@ -310,7 +312,7 @@ namespace osmium {
                     throw std::length_error("OSM user name is too long");
                 }
                 comment.set_user_size(osmium::string_size_type(length) + 1);
-                add_size(append(user, osmium::memory::item_size_type(length)) + append_zero());
+                add_size(append_with_zero(user, osmium::memory::item_size_type(length)));
             }
 
             void add_text(osmium::ChangesetComment& comment, const char* text, const size_t length) {
@@ -322,7 +324,7 @@ namespace osmium {
                     throw std::length_error("OSM changeset comment is too long");
                 }
                 comment.set_text_size(osmium::string_size_type(length) + 1);
-                add_size(append(text, osmium::memory::item_size_type(length)) + append_zero());
+                add_size(append_with_zero(text, osmium::memory::item_size_type(length)));
                 add_padding(true);
             }