diff --git a/src/libmpg123/format.c b/src/libmpg123/format.c
index 5350ed4e..c4457e35 100644
--- a/src/libmpg123/format.c
+++ b/src/libmpg123/format.c
@@ -688,7 +688,7 @@ static void conv_s16_to_s32(struct outbuffer *buf)
 
 #include "../common/swap_bytes_impl.h"
 
-void swap_endian(struct outbuffer *buf, int block)
+static void swap_endian(struct outbuffer *buf, int block)
 {
 	size_t count;
 
diff --git a/src/libmpg123/id3.c b/src/libmpg123/id3.c
index 180f489f..0bd5cda7 100644
--- a/src/libmpg123/id3.c
+++ b/src/libmpg123/id3.c
@@ -794,7 +794,7 @@ static int promote_framename(mpg123_handle *fr, char *id) /* fr because of VERBO
 
 #endif /* NO_ID3V2 */
 
-int store_id3v2( mpg123_handle *fr
+static int store_id3v2( mpg123_handle *fr
 ,	unsigned long first4bytes, unsigned char buf[6], unsigned long length )
 {
 	int ret = 1;
diff --git a/src/libmpg123/optimize.c b/src/libmpg123/optimize.c
index 00e43c16..65c5a776 100644
--- a/src/libmpg123/optimize.c
+++ b/src/libmpg123/optimize.c
@@ -1027,7 +1027,7 @@ static const char *mpg123_decoder_list[] =
 	NULL
 };
 
-void check_decoders(void)
+static void check_decoders(void)
 {
 #ifndef OPT_MULTI
 	/* In non-multi mode, only the full list (one entry) is used. */