diff --git a/changes/bug5621 b/changes/bug5621
new file mode 100644
index 0000000000..1ffc6042c5
--- /dev/null
+++ b/changes/bug5621
@@ -0,0 +1,3 @@
+  o Minor enhancement:
+    - Document unit of bandwidth related options in sample torrc.
+      Fixes bug 5621.
diff --git a/src/config/torrc.bridge.in b/src/config/torrc.bridge.in
index 927c7bbba2..b7b7e050ba 100644
--- a/src/config/torrc.bridge.in
+++ b/src/config/torrc.bridge.in
@@ -96,6 +96,8 @@ Nickname Unnamed
 ## Define these to limit how much relayed traffic you will allow. Your
 ## own traffic is still unthrottled. Note that RelayBandwidthRate must
 ## be at least 20 KB.
+## Note that units for these config options are bytes per second, not bits
+## per second, and that prefixes are binary prefixes, i.e. 2^10, 2^20, etc.
 #RelayBandwidthRate 100 KB  # Throttle traffic to 100KB/s (800Kbps)
 #RelayBandwidthBurst 200 KB # But allow bursts up to 200KB/s (1600Kbps)
 RelayBandwidthBurst 10485760
diff --git a/src/config/torrc.sample.in b/src/config/torrc.sample.in
index 17e3f0b2a4..258c125460 100644
--- a/src/config/torrc.sample.in
+++ b/src/config/torrc.sample.in
@@ -102,6 +102,8 @@ SocksListenAddress 127.0.0.1 # accept connections only from localhost
 ## Define these to limit how much relayed traffic you will allow. Your
 ## own traffic is still unthrottled. Note that RelayBandwidthRate must
 ## be at least 20 KB.
+## Note that units for these config options are bytes per second, not bits
+## per second, and that prefixes are binary prefixes, i.e. 2^10, 2^20, etc.
 #RelayBandwidthRate 100 KB  # Throttle traffic to 100KB/s (800Kbps)
 #RelayBandwidthBurst 200 KB # But allow bursts up to 200KB/s (1600Kbps)