diff --git a/src/multimap.h b/src/multimap.h
index bd31735a..016a4513 100644
--- a/src/multimap.h
+++ b/src/multimap.h
@@ -33,7 +33,6 @@ SOFTWARE.
 
 #include <stddef.h>
 #include <iterator>
-#include <functional>
 #include <algorithm>
 #include <functional>
 
diff --git a/src/multiset.h b/src/multiset.h
index 753addeb..e01e1d59 100644
--- a/src/multiset.h
+++ b/src/multiset.h
@@ -33,7 +33,6 @@ SOFTWARE.
 
 #include <stddef.h>
 #include <iterator>
-#include <functional>
 #include <algorithm>
 #include <functional>
 
diff --git a/src/set.h b/src/set.h
index 27dc85f2..32f58a9d 100644
--- a/src/set.h
+++ b/src/set.h
@@ -33,7 +33,6 @@ SOFTWARE.
 
 #include <stddef.h>
 #include <iterator>
-#include <functional>
 #include <algorithm>
 #include <functional>