diff --git a/mlir/include/mlir/Pass/PassManager.h b/mlir/include/mlir/Pass/PassManager.h
--- a/mlir/include/mlir/Pass/PassManager.h
+++ b/mlir/include/mlir/Pass/PassManager.h
@@ -14,6 +14,7 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/iterator.h"
 
+#include <functional>
 #include <vector>
 
 namespace llvm {