diff --git a/pkg/agent/guardrail/prompt_injection.go b/pkg/agent/guardrail/prompt_injection.go
index 1ed0a0dc9..787f1c6d4 100644
--- a/pkg/agent/guardrail/prompt_injection.go
+++ b/pkg/agent/guardrail/prompt_injection.go
@@ -59,20 +59,20 @@ func (g *PromptInjectionGuardrail) Check(ctx context.Context, messages []llm.Mes
 	resp, err := g.client.ChatCompletion(
 		ctx,
 		&llm.ChatCompletionRequest{
-		Model: "gpt-4o-mini",
-		Messages: []llm.Message{
-			{
-				Role:  llm.RoleSystem,
-				Parts: []llm.Part{llm.TextPart{Text: promptInjectionClassifierPrompt}},
-			},
-			{
-				Role:  llm.RoleUser,
-				Parts: []llm.Part{llm.TextPart{Text: userText}},
+			Model: "gpt-4o-mini",
+			Messages: []llm.Message{
+				{
+					Role:  llm.RoleSystem,
+					Parts: []llm.Part{llm.TextPart{Text: promptInjectionClassifierPrompt}},
+				},
+				{
+					Role:  llm.RoleUser,
+					Parts: []llm.Part{llm.TextPart{Text: userText}},
+				},
 			},
+			MaxTokens:   new(10),
+			Temperature: new(0.0),
 		},
-		MaxTokens:   new(10),
-		Temperature: new(0.0),
-	},
 	)
 	if err != nil {
 		// If the classifier fails, allow the message through rather than
diff --git a/pkg/agent/guardrail/sensitive_data.go b/pkg/agent/guardrail/sensitive_data.go
index 96ecd778f..b3f4cbaaa 100644
--- a/pkg/agent/guardrail/sensitive_data.go
+++ b/pkg/agent/guardrail/sensitive_data.go
@@ -58,7 +58,8 @@ func (g *SensitiveDataGuardrail) Check(_ context.Context, message llm.Message) (
 		"sk_test_",
 
 		// LLM provider keys
-		"sk-",
+		"sk-proj-", // OpenAI
+		"sk-ant-",  // Anthropic
 
 		// JWT tokens
 		"eyj", // base64-encoded JSON header
diff --git a/pkg/agent/guardrail/sensitive_data_test.go b/pkg/agent/guardrail/sensitive_data_test.go
index 080714c35..fdcd4a31a 100644
--- a/pkg/agent/guardrail/sensitive_data_test.go
+++ b/pkg/agent/guardrail/sensitive_data_test.go
@@ -66,6 +66,8 @@ func TestSensitiveDataGuardrail_Check(t *testing.T) {
 
 		// LLM provider keys
 		{"openai key", "The API key is sk-proj-abc123", true},
+		{"anthropic key", "Key: sk-ant-api03-abc123", true},
+		{"sk prefix not a false positive", "This is a risk-based approach to task-management.", false},
 
 		// JWT tokens
 		{"jwt token", "Token: eyJhbGciOiJIUzI1NiJ9.payload.sig", true},
diff --git a/pkg/agent/guardrail/system_prompt_leak.go b/pkg/agent/guardrail/system_prompt_leak.go
index 61e69295c..271234895 100644
--- a/pkg/agent/guardrail/system_prompt_leak.go
+++ b/pkg/agent/guardrail/system_prompt_leak.go
@@ -27,9 +27,12 @@ type SystemPromptLeakGuardrail struct {
 }
 
 func NewSystemPromptLeakGuardrail(fingerprints []string) *SystemPromptLeakGuardrail {
-	lowered := make([]string, len(fingerprints))
-	for i, f := range fingerprints {
-		lowered[i] = strings.ToLower(f)
+	lowered := make([]string, 0, len(fingerprints))
+	for _, f := range fingerprints {
+		if f == "" {
+			continue
+		}
+		lowered = append(lowered, strings.ToLower(f))
 	}
 
 	return &SystemPromptLeakGuardrail{fingerprints: lowered}
diff --git a/pkg/agent/guardrail/system_prompt_leak_test.go b/pkg/agent/guardrail/system_prompt_leak_test.go
index 9967783be..ad2e762ae 100644
--- a/pkg/agent/guardrail/system_prompt_leak_test.go
+++ b/pkg/agent/guardrail/system_prompt_leak_test.go
@@ -66,4 +66,14 @@ func TestSystemPromptLeakGuardrail_Check(t *testing.T) {
 		require.NoError(t, err)
 		assert.False(t, result.Tripwire)
 	})
+
+	t.Run("empty fingerprints are ignored", func(t *testing.T) {
+		t.Parallel()
+
+		g := guardrail.NewSystemPromptLeakGuardrail([]string{"", "secret phrase", ""})
+		result, err := g.Check(context.Background(), assistantMessage("hello world"))
+
+		require.NoError(t, err)
+		assert.False(t, result.Tripwire)
+	})
 }