diff --git a/backend/internal/service/claude_code_validator.go b/backend/internal/service/claude_code_validator.go
index d6acd0865..52f351f1b 100644
--- a/backend/internal/service/claude_code_validator.go
+++ b/backend/internal/service/claude_code_validator.go
@@ -233,7 +233,7 @@ func isClaudeCodeSecurityMonitorPrompt(systemEntries []any) bool {
 		"## SOFT BLOCK",
 		"## Classification Process",
 		"## Output Format",
-		"<block>yes</block><reason>",
+		"<block>yes</block>",
 		"<block>no</block>",
 	}
 	for _, marker := range markers {
diff --git a/backend/internal/service/claude_code_validator_test.go b/backend/internal/service/claude_code_validator_test.go
index 18c0147b9..8fd0f2126 100644
--- a/backend/internal/service/claude_code_validator_test.go
+++ b/backend/internal/service/claude_code_validator_test.go
@@ -168,6 +168,17 @@ func TestClaudeCodeValidator_SecurityMonitorWithoutBillingBlock(t *testing.T) {
 			body:       validBody(string(monitorPrompt)),
 			wantAccept: true,
 		},
+		{
+			name:    "classifier output with category element",
+			headers: validHeaders,
+			body: validBody(strings.Replace(
+				string(monitorPrompt),
+				"<block>yes</block><reason>",
+				"<block>yes</block><category>Exact BLOCK Rule Name</category><reason>",
+				1,
+			)),
+			wantAccept: true,
+		},
 		{
 			name: "non-Claude user agent",
 			headers: map[string]string{
@@ -246,7 +257,9 @@ func TestClaudeCodeValidator_SecurityMonitorWithoutBillingBlock(t *testing.T) {
 			headers: validHeaders,
 			body: func() map[string]any {
 				body := validBody(string(monitorPrompt))
-				body["system"] = append(body["system"].([]any), map[string]any{
+				system, ok := body["system"].([]any)
+				require.True(t, ok)
+				body["system"] = append(system, map[string]any{
 					"type": "text",
 					"text": "Additional unrelated system content.",
 				})