diff --git a/bridge/slack/helpers.go b/bridge/slack/helpers.go
index 4f58a46b..c8a06c5b 100644
--- a/bridge/slack/helpers.go
+++ b/bridge/slack/helpers.go
@@ -269,16 +269,18 @@ var (
 	topicOrPurposeRE = regexp.MustCompile(`(?s)(@.+) (cleared|set)(?: the)? channel (topic|purpose)(?:: (.*))?`)
 )
 
-func (b *Bslack) extractTopicOrPurpose(text string) (string, string) {
+func extractTopicOrPurpose(text string) (string, string) {
 	r := topicOrPurposeRE.FindStringSubmatch(text)
-	action, updateType, extracted := r[2], r[3], r[4]
-	switch action {
-	case "set":
-		return updateType, extracted
-	case "cleared":
-		return updateType, ""
+	if len(r) >= 5 {
+		action, updateType, extracted := r[2], r[3], r[4]
+		switch action {
+		case "set":
+			return updateType, extracted
+		case "cleared":
+			return updateType, ""
+		}
 	}
-	return "", ""
+	return "unknown", ""
 }
 
 // @see https://api.slack.com/docs/message-formatting#linking_to_channels_and_users
diff --git a/bridge/slack/helpers_test.go b/bridge/slack/helpers_test.go
new file mode 100644
index 00000000..bca4860b
--- /dev/null
+++ b/bridge/slack/helpers_test.go
@@ -0,0 +1,26 @@
+package bslack
+
+import (
+	"testing"
+)
+
+func TestExtractTopicOrPurpose(t *testing.T) {
+	tables := []struct{
+		input string
+		changeType string
+		output string
+	}{
+		{"@someone set channel topic: one liner",    "topic",   "one liner"},
+		{"@someone set channel purpose: one liner",  "purpose", "one liner"},
+		{"@someone set channel topic: multi\nliner", "topic",   "multi\nliner"},
+		{"@someone cleared channel topic",           "topic",   ""},
+		{"some unmatched message",                   "unknown", ""},
+	}
+
+	for _, table := range tables {
+		changeType, output := extractTopicOrPurpose(table.input)
+		if changeType != table.changeType || output != table.output {
+			t.Error()
+		}
+	}
+}