diff --git a/index.html b/index.html
index 80bde0479..e2ea39a0b 100644
--- a/index.html
+++ b/index.html
@@ -87,6 +87,11 @@ there.
 could set
 `logging.level.org.springframework.web.servlet.DispatcherServlet=DEBUG`
 
+> NOTE: If you use Zipkin, configure the probability of spans exported by
+setting (for `2.0.x`) `spring.sleuth.sampler.probability` or
+(up till `2.0.x`)`spring.sleuth.sampler.percentage` (default: 0.1, which is 10 percent). 
+Otherwise, you might think that Sleuth is not working be cause it omits some spans.
+
 > NOTE: Set `spring.application.name=bar` (for instance) to see the
 service name as well as the trace and span ids.