diff --git a/include/nova/pomdp/utilities/pomdp_sigma_cpu.h b/include/nova/pomdp/utilities/pomdp_sigma_cpu.h
index d764b2b..a40a38a 100644
--- a/include/nova/pomdp/utilities/pomdp_sigma_cpu.h
+++ b/include/nova/pomdp/utilities/pomdp_sigma_cpu.h
@@ -29,6 +29,7 @@
 #include <nova/pomdp/pomdp.h>
 
 #include <utility>
+#include <vector>
 
 namespace nova {