diff --git a/src/auth/mech-rpa.c b/src/auth/mech-rpa.c
index 743b323f06..6cc2f9db74 100644
--- a/src/auth/mech-rpa.c
+++ b/src/auth/mech-rpa.c
@@ -381,7 +381,7 @@ mech_rpa_build_token2(struct rpa_auth_request *request, size_t *size)
 	buffer_append_c(buf, realms_len & 0xff);
 	buffer_append(buf, str_c(realms), realms_len);
 
-	*size = buffer_get_used_size(buf);
+	*size = buf->used;
 	return buffer_free_without_data(&buf);
 }
 
@@ -414,7 +414,7 @@ mech_rpa_build_token4(struct rpa_auth_request *request, size_t *size)
 	/* Status, 0 - success */
 	buffer_append_c(buf, 0);
 
-	*size = buffer_get_used_size(buf);
+	*size = buf->used;
 	return buffer_free_without_data(&buf);
 }
 
diff --git a/src/auth/password-scheme-rpa.c b/src/auth/password-scheme-rpa.c
index 1ea06b8350..d75f8d4c6b 100644
--- a/src/auth/password-scheme-rpa.c
+++ b/src/auth/password-scheme-rpa.c
@@ -20,7 +20,7 @@ void *ucs2be_str(pool_t pool, const char *str, size_t *size)
 		buffer_append_c(buf, *str++);
 	}
 
-	*size = buffer_get_used_size(buf);
+	*size = buf->used;
 	return buffer_free_without_data(&buf);
 }
 
diff --git a/src/lib-index/mail-transaction-log-file.c b/src/lib-index/mail-transaction-log-file.c
index a016caee9e..2e24d7c97d 100644
--- a/src/lib-index/mail-transaction-log-file.c
+++ b/src/lib-index/mail-transaction-log-file.c
@@ -1461,7 +1461,7 @@ mail_transaction_log_file_read_more(struct mail_transaction_log_file *file)
 	uint32_t read_offset;
 	ssize_t ret;
 
-	read_offset = file->buffer_offset + buffer_get_used_size(file->buffer);
+	read_offset = file->buffer_offset + file->buffer->used;
 
 	do {
 		data = buffer_append_space_unsafe(file->buffer, LOG_PREFETCH);
@@ -1707,7 +1707,7 @@ int mail_transaction_log_file_map(struct mail_transaction_log_file *file,
 
 	if (file->buffer != NULL && file->buffer_offset <= start_offset) {
 		/* see if we already have it */
-		size = buffer_get_used_size(file->buffer);
+		size = file->buffer->used;
 		if (file->buffer_offset + size >= end_offset)
 			return 1;
 	}
diff --git a/src/lib-mail/message-part-serialize.c b/src/lib-mail/message-part-serialize.c
index 3ab584e481..a5e74438ec 100644
--- a/src/lib-mail/message-part-serialize.c
+++ b/src/lib-mail/message-part-serialize.c
@@ -73,7 +73,7 @@ static void part_serialize(struct message_part *part, buffer_t *dest,
 
 		if ((part->flags & (MESSAGE_PART_FLAG_MULTIPART |
 				    MESSAGE_PART_FLAG_MESSAGE_RFC822)) != 0) {
-			children_offset = buffer_get_used_size(dest);
+			children_offset = dest->used;
 			children_count = 0;
 			buffer_append(dest, &children_count,
 				      sizeof(children_count));
diff --git a/src/lib-ntlm/ntlm-encrypt.c b/src/lib-ntlm/ntlm-encrypt.c
index 5c824912dc..28905429c3 100644
--- a/src/lib-ntlm/ntlm-encrypt.c
+++ b/src/lib-ntlm/ntlm-encrypt.c
@@ -29,7 +29,7 @@ t_unicode_str(const char *src, bool ucase, size_t *size)
 		buffer_append_c(wstr, '\0');
 	}
 
-	*size = buffer_get_used_size(wstr);
+	*size = wstr->used;
 	return buffer_free_without_data(&wstr);
 }
 
diff --git a/src/lib-ntlm/ntlm-message.c b/src/lib-ntlm/ntlm-message.c
index 0a5c55f622..6c18fd1e9d 100644
--- a/src/lib-ntlm/ntlm-message.c
+++ b/src/lib-ntlm/ntlm-message.c
@@ -61,7 +61,7 @@ static void ntlmssp_append_string(buffer_t *buf, size_t buffer_offset,
 	struct ntlmssp_buffer buffer;
 	unsigned int length;
 
-	write_le32(&buffer.offset, buffer_get_used_size(buf));
+	write_le32(&buffer.offset, buf->used);
 
 	length = append_string(buf, str, FALSE, unicode);
 
@@ -78,7 +78,7 @@ static void ntlmssp_append_target_info(buffer_t *buf, size_t buffer_offset, ...)
 	unsigned int length, total_length = 0;
 	int type;
 
-	write_le32(&buffer.offset, buffer_get_used_size(buf));
+	write_le32(&buffer.offset, buf->used);
 
 	va_start(args, buffer_offset);
 
@@ -169,7 +169,7 @@ ntlmssp_create_challenge(pool_t pool, const struct ntlmssp_request *request,
 				   NTPLMSSP_V2_TARGET_FQDN, my_hostname,
 				   NTPLMSSP_V2_TARGET_END);
 
-	*size = buffer_get_used_size(buf);
+	*size = buf->used;
 	return buffer_free_without_data(&buf);
 }
 
diff --git a/src/lib/str.c b/src/lib/str.c
index 8cfd5d207d..ba837d9c3b 100644
--- a/src/lib/str.c
+++ b/src/lib/str.c
@@ -80,7 +80,7 @@ char *str_c_modifiable(string_t *str)
 
 size_t str_len(const string_t *str)
 {
-	return buffer_get_used_size(str);
+	return str->used;
 }
 
 bool str_equals(const string_t *str1, const string_t *str2)