diff --git a/ApplicationLibCode/ReservoirDataModel/RigHistogramData.h b/ApplicationLibCode/ReservoirDataModel/RigHistogramData.h
index 0f16349177..5f9476a481 100644
--- a/ApplicationLibCode/ReservoirDataModel/RigHistogramData.h
+++ b/ApplicationLibCode/ReservoirDataModel/RigHistogramData.h
@@ -18,6 +18,7 @@
 
 #pragma once
 
+#include <cstddef>
 #include <vector>
 
 //==================================================================================================