diff --git a/algo/detectors/sts/UnpackSts.cxx b/algo/detectors/sts/UnpackSts.cxx
index 7753040e7d55f8811263bd40ce97f4a86a5a7f9b..77829fa0f7d6151fe716f84afa40823dd25a27bf 100644
--- a/algo/detectors/sts/UnpackSts.cxx
+++ b/algo/detectors/sts/UnpackSts.cxx
@@ -47,6 +47,9 @@ namespace cbm::algo
       return result;
     }
 
+    const u32 maxDigis = numMessages - 2;  // -2 for the TS_MSB and EPOCH messages
+    result.first.reserve(maxDigis);
+
     // --- Interpret MS content as sequence of SMX messages
     auto message = reinterpret_cast<const stsxyter::Message*>(msContent);