diff --git a/src/modbus-rtu.c b/src/modbus-rtu.c
index 7aa3852..6251f7d 100644
--- a/src/modbus-rtu.c
+++ b/src/modbus-rtu.c
@@ -1151,6 +1151,7 @@ modbus_t* modbus_new_rtu(const char *device,
     ctx->backend = &_modbus_rtu_backend;
     ctx->backend_data = (modbus_rtu_t *) malloc(sizeof(modbus_rtu_t));
     ctx_rtu = (modbus_rtu_t *)ctx->backend_data;
+    ctx_rtu->device = NULL;
 
     /* Check device argument */
     if (device == NULL || (*device) == 0) {
diff --git a/tests/unit-test-client.c b/tests/unit-test-client.c
index 1df9d79..21cab0c 100644
--- a/tests/unit-test-client.c
+++ b/tests/unit-test-client.c
@@ -835,6 +835,16 @@ int main(int argc, char *argv[])
         goto close;
     }
 
+    /* Test init functions */
+    printf("\nTEST INVALID INITIALIZATION:\n");
+    ctx = modbus_new_rtu(NULL, 0, 'A', 0, 0);
+    if (ctx == NULL && errno == EINVAL) {
+        printf("OK\n");
+    } else {
+        printf("FAILED\n");
+        goto close;
+    }
+
     printf("\nALL TESTS PASS WITH SUCCESS.\n");
 
 close: