diff --git a/src/llc.c b/src/llc.c
index ddc1e03..c283146 100644
--- a/src/llc.c
+++ b/src/llc.c
@@ -80,7 +80,7 @@
 	llc->length += len;
 }
 
-bool llc_is_user_data_frame(const uint8_t *data, size_t len)
+static bool llc_is_user_data_frame(const uint8_t *data, size_t len)
 {
 	if (len < 2)
 		return false;
diff --git a/src/llc.h b/src/llc.h
index fe14c6a..58b169e 100644
--- a/src/llc.h
+++ b/src/llc.h
@@ -58,7 +58,6 @@
 	uint16_t index; /* current write/read position of frame */
 	uint16_t length; /* len of current DL LLC_frame, 0 == no frame */
 };
-bool llc_is_user_data_frame(const uint8_t *data, size_t len);
 
 void llc_init(struct gprs_llc *llc);
 void llc_reset(struct gprs_llc *llc);