diff --git a/Makefile b/Makefile
index 583bc25bc6..e8bcd4edd1 100644
--- a/Makefile
+++ b/Makefile
@@ -129,9 +129,12 @@ CFLAGS += -Wno-unused-but-set-variable
 endif
 else
 $(info $(MSG_PREFIX)Found GCC_MAJOR>=5)
+CLANG_HEADER=$(shell $(CC) --version | grep -w clang)
+ifeq (,$(CLANG_HEADER))
 CFLAGS += -Wno-unused-but-set-variable
 endif
 endif
+endif
 
 endif
 
diff --git a/src/base/io/io.c b/src/base/io/io.c
index c2363cb520..d483bbf6ee 100644
--- a/src/base/io/io.c
+++ b/src/base/io/io.c
@@ -18,6 +18,7 @@
 
 ***********************************************************************/
 
+#include <unistd.h>
 #include "ioAbc.h"
 #include "base/main/mainInt.h"
 #include "aig/saig/saig.h"