diff --git a/source/CircularQueueBuffer.hpp b/source/CircularQueueBuffer.hpp
index 349b3364da4c7e894f42e3d7711a4dd1b2fa3eed..c2e5efce96dde53d617ddebbbd15e8e542f85302 100644
--- a/source/CircularQueueBuffer.hpp
+++ b/source/CircularQueueBuffer.hpp
@@ -72,7 +72,7 @@ namespace com_saxbophone {
         /**
          * @returns the total capacity of this buffer
          */
-        constexpr size_t capacity() {
+        constexpr size_t capacity() const {
             return BUFFER_SIZE;
         }