diff --git a/lib/libc/string/swab.c b/lib/libc/string/swab.c
--- a/lib/libc/string/swab.c
+++ b/lib/libc/string/swab.c
@@ -4,19 +4,22 @@
  */
 
 #include <unistd.h>
+#include <sys/endian.h>
 
 void
 swab(const void * __restrict from, void * __restrict to, ssize_t len)
 {
-	const unsigned char *f = from;
-	unsigned char *t = to;
+	const uint16_t *f __aligned(1) = from;
+	uint16_t *t __aligned(1) = to;
 
+	/*
+	 * POSIX says overlapping copy behavior is undefined, however many
+	 * applications assume the old FreeBSD and current GNU libc behavior
+	 * that will swap the bytes correctly when from == to. Reading both bytes
+	 * and swapping them before writing them back accomplishes this.
+	 */
 	while (len > 1) {
-		t[0] = f[1];
-		t[1] = f[0];
-
-		f += 2;
-		t += 2;
+		*t++ = bswap16(*f++);
 		len -= 2;
 	}
 }