Do not use unistd.h on Windows; include process.h for getpid().
diff --git a/lib/mkstemp.c b/lib/mkstemp.c
index 57d8848..cdfc0e2 100644
--- a/lib/mkstemp.c
+++ b/lib/mkstemp.c
@@ -39,11 +39,13 @@
 #include <errno.h>
 #include <fcntl.h>
 #ifdef _WIN32
+#include <process.h>
 #include <io.h>
+#else
+#include <unistd.h>
 #endif
 #include <stdio.h>
 #include <stdlib.h>
-#include <unistd.h>
 
 #ifndef O_BINARY
 #define O_BINARY 0