diff --git a/configure b/configure
index dfcded4..9075b97 100755
--- a/configure
+++ b/configure
@@ -6310,6 +6310,7 @@ case "$host" in
        LIBS="$LIBS -framework OpenGL"
        LIBS="$LIBS -framework OpenAL"
        build_macosx="yes"
+       CFLAGS="$CFLAGS -DHAVE_UNISTD_H"
        ;;
     *-*-cygwin* | *-*-mingw32*)
        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for main in -lopengl32" >&5
diff --git a/configure.ac b/configure.ac
index 20a6d09..3a89aff 100644
--- a/configure.ac
+++ b/configure.ac
@@ -140,6 +140,7 @@ case "$host" in
        LIBS="$LIBS -framework OpenGL"
        LIBS="$LIBS -framework OpenAL"
        build_macosx="yes"
+       CFLAGS="$CFLAGS -DHAVE_UNISTD_H"
        ;;
     *-*-cygwin* | *-*-mingw32*)
        AC_CHECK_LIB([opengl32], [main], [], \
diff --git a/src/slirp/slirp.h b/src/slirp/slirp.h
index 416b402..6e15943 100644
--- a/src/slirp/slirp.h
+++ b/src/slirp/slirp.h
@@ -80,6 +80,10 @@ typedef char *SLIRPcaddr_t;
 # include <stdint.h>
 #endif
 
+#ifdef HAVE_UNISTD_H
+# include <unistd.h>
+#endif
+
 #ifndef _MSC_VER
 #include <sys/time.h>
 #else