diff --git a/MultiSource/Applications/ClamAV/zlib/zconf.h b/MultiSource/Applications/ClamAV/zlib/zconf.h
index 5e1d68a..0a15e15 100644
--- a/MultiSource/Applications/ClamAV/zlib/zconf.h
+++ b/MultiSource/Applications/ClamAV/zlib/zconf.h
@@ -8,6 +8,9 @@
 #ifndef ZCONF_H
 #define ZCONF_H
 
+/* Modified for llvm test-suite: */
+#include <unistd.h>
+
 /*
  * If you *really* need a unique prefix for all types and library functions,
  * compile with -DZ_PREFIX. The "standard" zlib should be compiled without it.