diff --git a/tool/pkcs12.cc b/tool/pkcs12.cc
index f6d7d10cb..10ff630f4 100644
--- a/tool/pkcs12.cc
+++ b/tool/pkcs12.cc
@@ -16,6 +16,7 @@
 #include <string>
 #include <vector>
 
+#include <errno.h>
 #include <fcntl.h>
 #include <stdint.h>
 #include <sys/stat.h>