diff --git a/workflow/inproc/observability_test.go b/workflow/inproc/observability_test.go
index 481fc00e..17edb7a9 100644
--- a/workflow/inproc/observability_test.go
+++ b/workflow/inproc/observability_test.go
@@ -4,15 +4,26 @@ package inproc_test
 
 import (
 	"context"
+	"errors"
+	"fmt"
 	"strings"
 	"testing"
 
 	"github.com/microsoft/agent-framework-go/workflow"
 	"github.com/microsoft/agent-framework-go/workflow/inproc"
+	internalobservability "github.com/microsoft/agent-framework-go/workflow/internal/observability"
 	"github.com/microsoft/agent-framework-go/workflow/internal/workflowtest"
 	"github.com/microsoft/agent-framework-go/workflow/observability"
 )
 
+type unserializablePayload struct {
+	Value string
+}
+
+func (unserializablePayload) MarshalJSON() ([]byte, error) {
+	return nil, errors.New("marshal failed")
+}
+
 func TestObservability_CreatesWorkflowEndToEndSpans(t *testing.T) {
 	tracer := workflowtest.NewRecordingTracer()
 	wf := newTelemetryWorkflow(t, tracer, workflow.TelemetryOptions{})
@@ -194,6 +205,49 @@ func TestObservability_SensitiveDataControlsMessageContent(t *testing.T) {
 	}
 }
 
+func TestObservability_UnserializableSensitiveDataDoesNotFailWorkflow(t *testing.T) {
+	tracer := workflowtest.NewRecordingTracer()
+	var received []unserializablePayload
+	start := workflow.NewExecutor("start", func(input string) unserializablePayload {
+		return unserializablePayload{Value: strings.ToUpper(input)}
+	}).Bind()
+	sink := workflow.NewExecutor("sink", func(msg unserializablePayload) string {
+		received = append(received, msg)
+		return "done"
+	}).Bind()
+
+	wf, err := workflow.NewBuilder(start).
+		AddEdge(start, sink).
+		WithOutputFrom(sink).
+		WithTelemetry(tracer, workflow.TelemetryOptions{EnableSensitiveData: true}).
+		Build()
+	if err != nil {
+		t.Fatalf("Build: %v", err)
+	}
+
+	run, err := inproc.Default.Run(context.Background(), wf, "hello")
+	if err != nil {
+		t.Fatalf("Run: %v", err)
+	}
+	outputs := collectOutputValues(run.OutgoingEvents())
+	if err := run.Close(context.Background()); err != nil {
+		t.Fatalf("Close: %v", err)
+	}
+
+	if len(outputs) != 1 || outputs[0] != "done" {
+		t.Fatalf("outputs = %#v, want []string{\"done\"}", outputs)
+	}
+	if len(received) != 1 || received[0].Value != "HELLO" {
+		t.Fatalf("received = %#v, want one delivered payload with value HELLO", received)
+	}
+
+	wantFallback := fmt.Sprintf("[Unserializable: %T]", unserializablePayload{})
+	messageSpan := workflowtest.FindSpanWithPrefix(t, tracer.Spans(), "message.send")
+	messageSpan.RequireAttributeValue(t, internalobservability.TagMessageContent, wantFallback)
+	sinkSpan := workflowtest.FindSpanWithPrefix(t, tracer.Spans(), "executor.process sink")
+	sinkSpan.RequireAttributeValue(t, internalobservability.TagExecutorInput, wantFallback)
+}
+
 func TestObservability_RunSpansAreEnded(t *testing.T) {
 	tests := []struct {
 		name string
diff --git a/workflow/internal/observability/observability_test.go b/workflow/internal/observability/observability_test.go
index 68898f0f..b0534295 100644
--- a/workflow/internal/observability/observability_test.go
+++ b/workflow/internal/observability/observability_test.go
@@ -13,6 +13,12 @@ import (
 	workflowobservability "github.com/microsoft/agent-framework-go/workflow/observability"
 )
 
+type unserializableValue struct{}
+
+func (unserializableValue) MarshalJSON() ([]byte, error) {
+	return nil, errors.New("marshal failed")
+}
+
 func attributeValue(t *testing.T, attrs []workflowobservability.Attribute, key string) string {
 	t.Helper()
 	for _, attr := range attrs {
@@ -112,3 +118,38 @@ func TestStartExecutorProcessEmitsExecutorType(t *testing.T) {
 		}
 	}
 }
+
+func TestSerializedAttributeUsesFallbackForMarshalErrors(t *testing.T) {
+	attr := observability.SerializedAttribute("message.content", unserializableValue{})
+	value, ok := attr.Value.(string)
+	if !ok {
+		t.Fatalf("attribute value type = %T, want string", attr.Value)
+	}
+	want := "[Unserializable: observability_test.unserializableValue]"
+	if value != want {
+		t.Fatalf("attribute value = %q, want %q", value, want)
+	}
+}
+
+func TestSensitiveDataUsesFallbackForExecutorInputAndOutput(t *testing.T) {
+	span := &fakeSpan{}
+	telemetry := observability.New(observability.Options{
+		Tracer:              &fakeTracer{span: span},
+		EnableSensitiveData: true,
+	})
+
+	message := unserializableValue{}
+	_, activity := telemetry.StartExecutorProcess(context.Background(), "exec1", "pkg.Type", "message", message, nil)
+	if activity == nil {
+		t.Fatal("expected an activity span")
+	}
+	telemetry.SetExecutorOutput(activity, message)
+
+	want := "[Unserializable: observability_test.unserializableValue]"
+	if got := attributeValue(t, span.attrs, observability.TagExecutorInput); got != want {
+		t.Fatalf("executor.input = %q, want %q", got, want)
+	}
+	if got := attributeValue(t, span.attrs, observability.TagExecutorOutput); got != want {
+		t.Fatalf("executor.output = %q, want %q", got, want)
+	}
+}