diff --git a/signalfx-org-metrics/metrics.yaml b/signalfx-org-metrics/metrics.yaml
index 3c3d979a..72eaa558 100644
--- a/signalfx-org-metrics/metrics.yaml
+++ b/signalfx-org-metrics/metrics.yaml
@@ -154,8 +154,12 @@ sf.org.apm.numSpansDroppedInvalid:
   brief: The number of invalid spans Splunk APM receives.
   description: |
     The number of invalid spans Splunk APM receives. A span can be
-    invalid if there is no start time, trace ID, or service associated with it,
-    or if there are too many spans in the trace.
+    invalid for the following reasons: if there is no start time, trace ID, or service associated with it.
+      * invalidTraceID: Trace ID isn't a 16-byte or 32-byte hex number
+      * noOperationName: No operation name was provided
+      * spanTooLarge: Span body exceeds 64KiB
+      * zeroStartTime: The start timestamp is 0
+      * zipkinV2BinaryAnnotations: Unsupported Zipkin feature
 
       * Dimension(s): `orgId`
       * Data resolution: 1 second