diff --git a/libc/bionic/sigfillset.cpp b/libc/bionic/sigfillset.cpp
index 37792e5..cb67394 100644
--- a/libc/bionic/sigfillset.cpp
+++ b/libc/bionic/sigfillset.cpp
@@ -28,6 +28,7 @@
 
 #include <errno.h>
 #include <signal.h>
+#include <string.h>
 
 int sigfillset(sigset_t* set) {
   if (set == NULL) {