diff --git a/openbsc/tests/sgsn/Makefile.am b/openbsc/tests/sgsn/Makefile.am
index e3cec50..b6036c7 100644
--- a/openbsc/tests/sgsn/Makefile.am
+++ b/openbsc/tests/sgsn/Makefile.am
@@ -7,6 +7,7 @@
 
 sgsn_test_SOURCES = sgsn_test.c
 sgsn_test_LDFLAGS = \
+	-Wl,--wrap=RAND_bytes \
 	-Wl,--wrap=sgsn_update_subscriber_data \
 	-Wl,--wrap=gprs_subscr_request_update_location \
 	-Wl,--wrap=gprs_subscr_request_auth_info \
diff --git a/openbsc/tests/sgsn/sgsn_test.c b/openbsc/tests/sgsn/sgsn_test.c
index d568807..e8e05f6 100644
--- a/openbsc/tests/sgsn/sgsn_test.c
+++ b/openbsc/tests/sgsn/sgsn_test.c
@@ -101,6 +101,25 @@
 	return 0;
 }
 
+/* override, requires '-Wl,--wrap=RAND_bytes' */
+int __real_RAND_bytes(unsigned char *buf, int num);
+int mock_RAND_bytes(unsigned char *buf, int num);
+int (*RAND_bytes_cb)(unsigned char *, int) =
+  &mock_RAND_bytes;
+
+int __wrap_RAND_bytes(unsigned char *buf, int num)
+{
+	return (*RAND_bytes_cb)(buf, num);
+}
+/* make results of A&C ref predictable */
+int mock_RAND_bytes(unsigned char *buf, int num)
+{
+	if (num > 1)
+		return __real_RAND_bytes(buf, num);
+	buf[0] = 0;
+	return 1;
+}
+
 /* override, requires '-Wl,--wrap=sgsn_update_subscriber_data' */
 void __real_sgsn_update_subscriber_data(struct sgsn_mm_ctx *);
 void (*update_subscriber_data_cb)(struct sgsn_mm_ctx *) =