diff --git a/mlir/include/mlir/Support/StringExtras.h b/mlir/include/mlir/Support/StringExtras.h
index a5ec73275ff6..9948d15011a7 100644
--- a/mlir/include/mlir/Support/StringExtras.h
+++ b/mlir/include/mlir/Support/StringExtras.h
@@ -24,6 +24,8 @@
 
 #include "llvm/ADT/StringExtras.h"
 
+#include <cctype>
+
 namespace mlir {
 /// Converts a string to snake-case from camel-case by replacing all uppercase
 /// letters with '_' followed by the letter in lowercase, except if the
diff --git a/mlir/unittests/IR/StringExtrasTest.cpp b/mlir/unittests/IR/StringExtrasTest.cpp
index 6d18633dd9c3..def659503653 100644
--- a/mlir/unittests/IR/StringExtrasTest.cpp
+++ b/mlir/unittests/IR/StringExtrasTest.cpp
@@ -1,4 +1,4 @@
-//===- StringExtras.cpp - Tests for utility methods in StringExtras.h -----===//
+//===- StringExtrasTest.cpp - Tests for utility methods in StringExtras.h -===//
 //
 // Copyright 2019 The MLIR Authors.
 //