diff --git a/test/printf-test.cc b/test/printf-test.cc
index a0c86245..55aa6593 100644
--- a/test/printf-test.cc
+++ b/test/printf-test.cc
@@ -25,6 +25,7 @@
  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <cctype>
 #include <climits>
 #include <cstring>