diff --git a/src/algorithms/digi/PulseCombiner.cc b/src/algorithms/digi/PulseCombiner.cc
index 035e1d47d0..452de057f4 100644
--- a/src/algorithms/digi/PulseCombiner.cc
+++ b/src/algorithms/digi/PulseCombiner.cc
@@ -15,6 +15,7 @@
 #include <podio/RelationRange.h>
 #include <algorithm>
 #include <cmath>
+#include <cstddef>
 #include <gsl/pointers>
 #include <map>
 #include <numeric>