diff --git a/src/opt/opt_parse.cpp b/src/opt/opt_parse.cpp
index 29e8a604c0b..78ce8bd8503 100644
--- a/src/opt/opt_parse.cpp
+++ b/src/opt/opt_parse.cpp
@@ -69,7 +69,7 @@ class opt_stream_buffer {
 bool opt_stream_buffer::parse_token(char const* token) {
     skip_whitespace();
     char const* t = token;
-    while (ch() == *t) {
+    while (*t && ch() == *t) {
         next();
         ++t;
     }