diff --git a/utils/fwparam_ibft/fwparam_ppc.c b/utils/fwparam_ibft/fwparam_ppc.c
index b040837..6d344d1 100644
--- a/utils/fwparam_ibft/fwparam_ppc.c
+++ b/utils/fwparam_ibft/fwparam_ppc.c
@@ -436,10 +436,14 @@ int fwparam_ppc(struct boot_context *context, const char *filepath)
 	 * the appropriate FCODE with a load method.
 	 */
 	if (filepath) {
-		strncat(filename, filepath, FILENAMESZ);
+		strncat(filename, filepath, FILENAMESZ - 1);
+		filename[FILENAMESZ - 1] = '\0';
 		fplen = strlen(filename);
-	} else
-		strncat(filename, DT_TOP, FILENAMESZ);
+	} else {
+		strncat(filename, DT_TOP, FILENAMESZ - 1);
+		filename[FILENAMESZ - 1] = '\0';
+		fplen = strlen(filename);
+	}
 
 	strncat(filename + fplen, BOOTPATH, FILENAMESZ - fplen);