diff --git a/libc/bionic/sigemptyset.cpp b/libc/bionic/sigemptyset.cpp
index 2993169..8d8033f 100644
--- a/libc/bionic/sigemptyset.cpp
+++ b/libc/bionic/sigemptyset.cpp
@@ -26,6 +26,7 @@
  * SUCH DAMAGE.
  */
 
+#include <errno.h>
 #include <signal.h>
 
 int sigemptyset(sigset_t* set) {