diff --git a/site_ansto/tclClock.c b/site_ansto/tclClock.c
index 89815997..5b2ad530 100644
--- a/site_ansto/tclClock.c
+++ b/site_ansto/tclClock.c
@@ -1 +1,2 @@
+#define HAVE_UNISTD_H
 #include "../psi/tclClock.c"
diff --git a/site_ansto/tclDate.c b/site_ansto/tclDate.c
index aecaccb7..101791d3 100644
--- a/site_ansto/tclDate.c
+++ b/site_ansto/tclDate.c
@@ -1 +1,2 @@
+#define HAVE_UNISTD_H
 #include "../psi/tclDate.c"
diff --git a/site_ansto/tclUnixTime.c b/site_ansto/tclUnixTime.c
index 47d37302..c7e44144 100644
--- a/site_ansto/tclUnixTime.c
+++ b/site_ansto/tclUnixTime.c
@@ -1 +1,2 @@
+#define HAVE_UNISTD_H
 #include "../psi/tclUnixTime.c"