diff --git a/newlib/libc/string/swab.c b/newlib/libc/string/swab.c
index 82483371c..aee076319 100644
--- a/newlib/libc/string/swab.c
+++ b/newlib/libc/string/swab.c
@@ -21,7 +21,7 @@ PORTABILITY
 <<swab>> requires no supporting OS subroutines.
 */
 
-#include <string.h>
+#include <unistd.h>
 
 void
 _DEFUN (swab, (b1, b2, length),