diff --git a/test_h25.c b/test_h25.c
index bd37a3b..3a14d9b 100644
--- a/test_h25.c
+++ b/test_h25.c
@@ -79,7 +79,7 @@ bool test_h25(bool fast_flag, bool quiet_flag) {
     long i;
     for (i=0; i<100000; i++) {
         char message[30];
-        sprintf( message, "Message %ld", i );
+        snprintf( message, sizeof message, "Message %ld", i );
         unsigned message_len = strlen(message);
         bool success = hss_generate_signature( w, NULL, privkey,
                       message, message_len,
diff --git a/test_keyload.c b/test_keyload.c
index df278ec..3d22f44 100644
--- a/test_keyload.c
+++ b/test_keyload.c
@@ -122,7 +122,7 @@ if (len_signature == 0) return false;
 
         /* Generate a bunch of signatures of the same text */
         char text[ 100 ];
-        unsigned len_text = sprintf( text, "Message #%d", i );
+        unsigned len_text = snprintf( text, sizeof text, "Message #%d", i );
 
         if (!hss_generate_signature( w[0], NULL, private_key,
                 text, len_text,
diff --git a/test_reserve.c b/test_reserve.c
index 84fd748..b31fe89 100644
--- a/test_reserve.c
+++ b/test_reserve.c
@@ -170,7 +170,7 @@ bool test_reserve(bool fast_flag, bool quiet_flag) {
                 }
             }
             char message[ 100 ];
-            size_t len_message = sprintf( message, "Message #%d", i );
+            size_t len_message = snprintf( message, sizeof message, "Message #%d", i );
             got_update = false;
             struct hss_extra_info info = { 0 };
             unsigned char signature[ 16000 ];