diff --git a/src/commands/CmdUnique.cpp b/src/commands/CmdUnique.cpp
index db4716761..93207e415 100644
--- a/src/commands/CmdUnique.cpp
+++ b/src/commands/CmdUnique.cpp
@@ -26,6 +26,7 @@
 
 #include <cmake.h>
 #include <iostream>
+#include <string>
 #include <set>
 #include <algorithm>
 #include <Context.h>