diff --git a/src/tbf.cpp b/src/tbf.cpp
index aec67e7e..9c1dac9c 100644
--- a/src/tbf.cpp
+++ b/src/tbf.cpp
@@ -298,7 +298,7 @@ const gprs_llc_queue *gprs_rlcmac_tbf::llc_queue() const
 	return m_ms ? m_ms->llc_queue() : NULL;
 }
 
-int gprs_rlcmac_tbf::llc_queue_size() const
+size_t gprs_rlcmac_tbf::llc_queue_size() const
 {
 	/* m_ms->llc_queue() never returns NULL: GprsMs::m_llc_queue is a
 	 * member instance. */
diff --git a/src/tbf.h b/src/tbf.h
index 40ed9742..4a304afe 100644
--- a/src/tbf.h
+++ b/src/tbf.h
@@ -228,7 +228,7 @@ struct gprs_rlcmac_tbf {
 	uint8_t ms_class() const;
 	void set_ms_class(uint8_t);
 	GprsCodingScheme current_cs() const;
-	int llc_queue_size() const;
+	size_t llc_queue_size() const;
 
 	time_t created_ts() const;
 	uint8_t dl_slots() const;