diff --git a/include/graphblas/reference/coordinates.hpp b/include/graphblas/reference/coordinates.hpp
index 59ea0326f..56f8935ff 100644
--- a/include/graphblas/reference/coordinates.hpp
+++ b/include/graphblas/reference/coordinates.hpp
@@ -25,6 +25,7 @@
 
 #include <stddef.h> //size_t
 
+#include <cstdint>
 #include <stdexcept> //std::runtime_error
 
 #include <assert.h>
diff --git a/include/graphblas/reference/init.hpp b/include/graphblas/reference/init.hpp
index 9332c8b88..fb1393988 100644
--- a/include/graphblas/reference/init.hpp
+++ b/include/graphblas/reference/init.hpp
@@ -24,6 +24,7 @@
 #define _H_GRB_REFERENCE_INIT
 
 #include <new>
+#include <cstdint>
 #include <algorithm>
 
 #include <graphblas/base/init.hpp>