diff --git a/programs/cipher/cipher_aead_demo.c b/programs/cipher/cipher_aead_demo.c
index 853ec202c6f8..83fcce5878fe 100644
--- a/programs/cipher/cipher_aead_demo.c
+++ b/programs/cipher/cipher_aead_demo.c
@@ -79,7 +79,7 @@ const unsigned char msg2_part2[] = { 0x15, 0x16, 0x17 };
 const unsigned char key_bytes[32] = { 0x2a };
 
 /* Print the contents of a buffer in hex */
-void print_buf(const char *title, unsigned char *buf, size_t len)
+static void print_buf(const char *title, unsigned char *buf, size_t len)
 {
     printf("%s:", title);
     for (size_t i = 0; i < len; i++) {
diff --git a/programs/hash/md_hmac_demo.c b/programs/hash/md_hmac_demo.c
index 4b5aa3ba78c1..494e9efaa45b 100644
--- a/programs/hash/md_hmac_demo.c
+++ b/programs/hash/md_hmac_demo.c
@@ -57,7 +57,7 @@ const unsigned char msg2_part2[] = { 0x06, 0x06 };
 const unsigned char key_bytes[32] = { 0 };
 
 /* Print the contents of a buffer in hex */
-void print_buf(const char *title, unsigned char *buf, size_t len)
+static void print_buf(const char *title, unsigned char *buf, size_t len)
 {
     printf("%s:", title);
     for (size_t i = 0; i < len; i++) {
diff --git a/programs/psa/aead_demo.c b/programs/psa/aead_demo.c
index 619166dba488..2d99e3cbec59 100644
--- a/programs/psa/aead_demo.c
+++ b/programs/psa/aead_demo.c
@@ -82,7 +82,7 @@ const unsigned char msg2_part2[] = { 0x15, 0x16, 0x17 };
 const unsigned char key_bytes[32] = { 0x2a };
 
 /* Print the contents of a buffer in hex */
-void print_buf(const char *title, uint8_t *buf, size_t len)
+static void print_buf(const char *title, uint8_t *buf, size_t len)
 {
     printf("%s:", title);
     for (size_t i = 0; i < len; i++) {
diff --git a/programs/psa/hmac_demo.c b/programs/psa/hmac_demo.c
index f44f9a742f3f..683f3e59c9c6 100644
--- a/programs/psa/hmac_demo.c
+++ b/programs/psa/hmac_demo.c
@@ -59,7 +59,7 @@ const unsigned char msg2_part2[] = { 0x06, 0x06 };
 const unsigned char key_bytes[32] = { 0 };
 
 /* Print the contents of a buffer in hex */
-void print_buf(const char *title, uint8_t *buf, size_t len)
+static void print_buf(const char *title, uint8_t *buf, size_t len)
 {
     printf("%s:", title);
     for (size_t i = 0; i < len; i++) {