diff --git a/metrics/metrics.go b/metrics/metrics.go
index bd73126..3966d23 100644
--- a/metrics/metrics.go
+++ b/metrics/metrics.go
@@ -9,6 +9,10 @@ import (
 	"time"
 )
 
+// Fields must be in this order because go compiler has problems with 64bit fields on 32 bit arches (arm32 raspberry pi):
+//   https://git.openprivacy.ca/cwtch.im/server/pulls/30
+//   https://github.com/golang/go/issues/599
+//   https://github.com/census-instrumentation/opencensus-go/issues/587
 type counter struct {
 	count     uint64
 	startTime time.Time