diff --git a/usage.c b/usage.c
index e4fa6d2f03..50a6ccee44 100644
--- a/usage.c
+++ b/usage.c
@@ -12,7 +12,13 @@ void vreportf(const char *prefix, const char *err, va_list params)
 {
 	char msg[4096];
 	FILE *fh = error_handle ? error_handle : stderr;
+	char *p;
+
 	vsnprintf(msg, sizeof(msg), err, params);
+	for (p = msg; *p; p++) {
+		if (iscntrl(*p) && *p != '\t' && *p != '\n')
+			*p = '?';
+	}
 	fprintf(fh, "%s%s\n", prefix, msg);
 }