diff --git a/include/token_authorization_middleware.hpp b/include/token_authorization_middleware.hpp
index bbbaa15..8099020 100644
--- a/include/token_authorization_middleware.hpp
+++ b/include/token_authorization_middleware.hpp
@@ -138,7 +138,7 @@
     if (start_index == std::string::npos) {
       return nullptr;
     }
-    start_index += sizeof("SESSION=");
+    start_index += sizeof("SESSION=") - 1;
     auto end_index = cookie_value.find(";", start_index);
     if (end_index == std::string::npos) {
       end_index = cookie_value.size();