diff --git a/src/boot.c b/src/boot.c
index 233d5cc..8687c95 100644
--- a/src/boot.c
+++ b/src/boot.c
@@ -556,13 +556,13 @@ void boot_screen() {
 
 		for (i = 0; i < boot_src_cnt; i++) {
 			if (bootable[i]) {
-				sprintf(message, "\e[93mF%d\e[37m-%s\n", i+1, boot_source_name(boot_chain[i]));
+				snprintf(message, 80, "\e[93mF%d\e[37m-%s\n", i+1, boot_source_name(boot_chain[i]));
 				chan_write(0, (uint8_t *)message, strlen(message));
 			}
 		}
 	}
 
-	sprintf(message, "\nPress \e[93mSPACE\e[37m for default.\n");
+	snprintf(message, 80, "\nPress \e[93mSPACE\e[37m for default.\n");
 	chan_write(0, (uint8_t *)message, strlen(message));
 
 	// Give the user time to press a key to select a boot source
diff --git a/src/dev/fsys.c b/src/dev/fsys.c
index 48000e4..3c5bed8 100644
--- a/src/dev/fsys.c
+++ b/src/dev/fsys.c
@@ -888,7 +888,7 @@ SYSTEMCALL short fsys_set_label(short drive, const char * label) {
 	}
 #endif
 
-    sprintf(buffer, "%d:%s", drive, label);
+    snprintf(buffer, 80, "%d:%s", drive, label);
     fres = f_setlabel(buffer);
     if (fres != FR_OK) {
         ERROR("fsys_setlabel: %d", fres);
@@ -911,7 +911,7 @@ SYSTEMCALL short fsys_mkfs(short drive, char * label) {
     char buffer[80];
     FRESULT fres;
 
-    sprintf(buffer, "%d:", drive);
+    snprintf(buffer, 80, "%d:", drive);
     fres = f_mkfs(buffer, 0, workspace, FF_MAX_SS * 4);
     if (fres != FR_OK) {
         ERROR("fsys_mkfs: %d", fres);