diff --git a/lib/skywalking/span.lua b/lib/skywalking/span.lua
index e2a8eec..c02bdb6 100644
--- a/lib/skywalking/span.lua
+++ b/lib/skywalking/span.lua
@@ -260,12 +260,13 @@
     return self
 end
 
-function Span:tag(key, value)
+function Span:tag(tagKey, tagValue)
     if self.is_noop then
         return self
     end
 
-    self.tags[key] = value
+    local tag = {key = tagKey, value = tagValue}
+    self.tags[#self.tags + 1] = tag
 
     return self
 end
diff --git a/lib/skywalking/span_test.lua b/lib/skywalking/span_test.lua
index a2265e0..462ea01 100644
--- a/lib/skywalking/span_test.lua
+++ b/lib/skywalking/span_test.lua
@@ -117,8 +117,8 @@
         span1:finishWithDuration(123)
         lu.assertEquals(span1.end_time, 1234690)
 
-        span1:tag("key", "value")
-        lu.assertEquals(span1.tags[1], {key='value'})
+        span1:tag("key1", "value1")
+        lu.assertEquals(span1.tags[1].value, 'value1')
 
         lu.assertEquals(#span1.refs, 1)
         lu.assertEquals(span1.refs[1].network_address, '127.0.0.1:8080')