diff --git a/include/sta/ConcreteLibrary.hh b/include/sta/ConcreteLibrary.hh
index 57aa1f39..f8b4b502 100644
--- a/include/sta/ConcreteLibrary.hh
+++ b/include/sta/ConcreteLibrary.hh
@@ -16,6 +16,8 @@
 
 #pragma once
 
+#include <functional>
+
 #include "DisallowCopyAssign.hh"
 #include "Vector.hh"
 #include "Map.hh"
diff --git a/include/sta/ConcreteNetwork.hh b/include/sta/ConcreteNetwork.hh
index b207f56d..1dde908b 100644
--- a/include/sta/ConcreteNetwork.hh
+++ b/include/sta/ConcreteNetwork.hh
@@ -16,6 +16,8 @@
 
 #pragma once
 
+#include <functional>
+
 #include "DisallowCopyAssign.hh"
 #include "Map.hh"
 #include "Set.hh"
diff --git a/include/sta/Network.hh b/include/sta/Network.hh
index 1f5e1b1a..1b1c66c5 100644
--- a/include/sta/Network.hh
+++ b/include/sta/Network.hh
@@ -16,6 +16,8 @@
 
 #pragma once
 
+#include <functional>
+
 #include "DisallowCopyAssign.hh"
 #include "Map.hh"
 #include "StringUtil.hh"