diff --git a/pkg/slack/app.go b/pkg/slack/app.go
index 3dfedbc..82bc47f 100644
--- a/pkg/slack/app.go
+++ b/pkg/slack/app.go
@@ -39,8 +39,15 @@ func (f ChannelInfo) String() string {
 	return fmt.Sprintf("%s with %s", f.ChannelID, f.Filter)
 }
 
-func (f ChannelInfo) ShouldSend(run *jobs.WorkflowRun) bool {
-	return f.Filter.Length() == 0 || f.Filter.Any(run)
+func (f ChannelInfo) ShouldSend(run *jobs.WorkflowRun) (bool, error) {
+	if f.Filter.Length() == 0 {
+		return true, nil
+	}
+	result, err := f.Filter.Any(run)
+	if err != nil {
+		return false, err
+	}
+	return result, nil
 }
 
 func NewApp(logger *zap.Logger, config *Config, store kv.Store) *App {
@@ -81,9 +88,13 @@ func (a *App) GetChannels(ctx context.Context, repo string) ([]ChannelInfo, erro
 
 		for _, channelString := range channelInfoStrings {
 			channelID, conclusionsString, _ := strings.Cut(channelString, ":")
-			var conclusions []string
-			for _, conclusion := range strings.Split(conclusionsString, ",") {
-				if len(conclusion) > 0 {
+			var conclusions []Conclusion
+			for _, conclusionString := range strings.Split(conclusionsString, ",") {
+				if len(conclusionString) > 0 {
+					conclusion, err := NewConclusionFromString(conclusionString)
+					if err != nil {
+						return nil, err
+					}
 					conclusions = append(conclusions, conclusion)
 				}
 			}
diff --git a/pkg/slack/filter.go b/pkg/slack/filter.go
index 931036d..061afb6 100644
--- a/pkg/slack/filter.go
+++ b/pkg/slack/filter.go
@@ -9,10 +9,23 @@ import (
 	"k8s.io/utils/strings/slices"
 )
 
+type Conclusion string
+
+const (
+	ConclusionActionRequired Conclusion = "action_required"
+	ConclusionCancelled      Conclusion = "cancelled"
+	ConclusionFailure        Conclusion = "failure"
+	ConclusionNeutral        Conclusion = "neutral"
+	ConclusionSuccess        Conclusion = "success"
+	ConclusionSkipped        Conclusion = "skipped"
+	ConclusionStale          Conclusion = "stale"
+	ConclusionTimedOut       Conclusion = "timed_out"
+)
+
 type MessageFilterRule struct {
-	Conclusions []string `json:"conclusions"`
-	Branches    []string `json:"branches"`
-	Workflows   []string `json:"workflows"`
+	Conclusions []Conclusion `json:"conclusions"`
+	Branches    []string     `json:"branches"`
+	Workflows   []string     `json:"workflows"`
 }
 
 type MessageFilter struct {
@@ -42,8 +55,8 @@ func (mf MessageFilter) Length() int {
 	return len(mf.Whitelists)
 }
 
-func (rule MessageFilterRule) Pass(run *jobs.WorkflowRun) bool {
-	if len(rule.Conclusions) > 0 && !slices.Contains(rule.Conclusions, run.Conclusion) {
+func (rule MessageFilterRule) Pass(run *jobs.WorkflowRun, conclusion Conclusion) bool {
+	if len(rule.Conclusions) > 0 && !lo.Contains(rule.Conclusions, conclusion) {
 		return false
 	}
 	if len(rule.Branches) > 0 && !slices.Contains(rule.Branches, run.Branch) {
@@ -55,23 +68,39 @@ func (rule MessageFilterRule) Pass(run *jobs.WorkflowRun) bool {
 	return true
 }
 
-func (mf MessageFilter) Any(run *jobs.WorkflowRun) bool {
+func (mf MessageFilter) Any(run *jobs.WorkflowRun) (bool, error) {
+	conclusion, err := NewConclusionFromString(run.Conclusion)
+	if err != nil {
+		return false, fmt.Errorf("Workflow run yielded invalid conclusion: %s", conclusion)
+	}
 	for _, rule := range mf.Whitelists {
-		if rule.Pass(run) {
-			return true
+		if rule.Pass(run, conclusion) {
+			return true, nil
 		}
 	}
-	return false
+	return false, nil
+}
+
+func NewConclusionFromString(str string) (Conclusion, error) {
+	switch str {
+	case "action_required":
+		return ConclusionActionRequired, nil
+	default:
+		return "", fmt.Errorf("unknown conclusion: %s", str)
+	}
 }
 
-func ParseConclusions(conclusions []string) ([]string, error) {
+func ParseConclusions(conclusionStrings []string) ([]Conclusion, error) {
 	// Ref: https://docs.github.com/en/rest/checks/runs?apiVersion=2022-11-28#create-a-check-run--parameters
-	conclusionsEnum := []string{"action_required", "cancelled", "failure", "neutral", "success", "skipped", "stale", "timed_out"}
+	// conclusionsEnum := []string{"action_required", "cancelled", "failure", "neutral", "success", "skipped", "stale", "timed_out"}
+	var conclusions []Conclusion
 	var unsupportedConclusions []string
-	for _, c := range conclusions {
-		if !slices.Contains(conclusionsEnum, c) {
-			unsupportedConclusions = append(unsupportedConclusions, c)
+	for _, c := range conclusionStrings {
+		conclusion, err := NewConclusionFromString(c)
+		if err != nil {
+			return nil, err
 		}
+		conclusions = append(conclusions, conclusion)
 	}
 
 	if len(unsupportedConclusions) > 0 {
@@ -81,7 +110,7 @@ func ParseConclusions(conclusions []string) ([]string, error) {
 	return conclusions, nil
 }
 
-func NewFilterRule(key string, values []string, conclusions []string) (*MessageFilterRule, error) {
+func NewFilterRule(key string, values []string, conclusions []Conclusion) (*MessageFilterRule, error) {
 	mfr := &MessageFilterRule{}
 	switch key {
 	case "conclusions":
@@ -92,10 +121,6 @@ func NewFilterRule(key string, values []string, conclusions []string) (*MessageF
 	default:
 		return nil, fmt.Errorf("unsupported filter type: %s", key)
 	}
-	conclusions, err := ParseConclusions(conclusions)
-	if err != nil {
-		return nil, err
-	}
 
 	mfr.Conclusions = conclusions
 	return mfr, nil
@@ -119,7 +144,13 @@ func ParseAsFilter(filterRuleStrings []string) (*MessageFilter, error) {
 				return nil, fmt.Errorf("duplicated conclusion strings; use commas to separate conclusions")
 			}
 
-			conclusions := strings.Split(definition[0], ",")
+			conclusionStrings := strings.Split(definition[0], ",")
+
+			conclusions, err := ParseConclusions(conclusionStrings)
+			if err != nil {
+				return nil, err
+			}
+
 			rule, err := NewFilterRule("conclusions", []string{}, conclusions)
 			if err != nil {
 				return nil, err
@@ -134,7 +165,7 @@ func ParseAsFilter(filterRuleStrings []string) (*MessageFilter, error) {
 			}
 
 			values := strings.Split(definition[1], ",")
-			rule, err := NewFilterRule(filterType, values, []string{})
+			rule, err := NewFilterRule(filterType, values, []Conclusion{})
 			if err != nil {
 				return nil, err
 			}
@@ -148,7 +179,13 @@ func ParseAsFilter(filterRuleStrings []string) (*MessageFilter, error) {
 			}
 
 			values := strings.Split(definition[1], ",")
-			conclusions := strings.Split(definition[2], ",")
+			conclusionStrings := strings.Split(definition[2], ",")
+
+			conclusions, err := ParseConclusions(conclusionStrings)
+			if err != nil {
+				return nil, err
+			}
+
 			rule, err := NewFilterRule(filterType, values, conclusions)
 			if err != nil {
 				return nil, err
diff --git a/pkg/slack/notifier.go b/pkg/slack/notifier.go
index fc9d2fa..4acde69 100644
--- a/pkg/slack/notifier.go
+++ b/pkg/slack/notifier.go
@@ -158,10 +158,19 @@ func (n *Notifier) notify(ctx context.Context, run *jobs.WorkflowRun) {
 	}
 
 	for _, channel := range channels {
-		if channel.ShouldSend(run) {
+		result, err := channel.ShouldSend(run)
+		if err != nil {
+			n.logger.Warn("failed to send message",
+				zap.Error(err),
+				zap.String("channelID", channel.ChannelID),
+			)
+			return
+		}
+		if !result {
 			return
 		}
-		err := n.app.SendMessage(ctx, channel.ChannelID, slack.MsgOptionAttachments(slackMsg))
+
+		err = n.app.SendMessage(ctx, channel.ChannelID, slack.MsgOptionAttachments(slackMsg))
 		if err != nil {
 			n.logger.Warn("failed to send message",
 				zap.Error(err),