diff --git a/workflow/util/util.go b/workflow/util/util.go
index 51be4cb90fa0..be5dc4db6e85 100644
--- a/workflow/util/util.go
+++ b/workflow/util/util.go
@@ -475,7 +475,7 @@ func AddParamToGlobalScope(wf *wfv1.Workflow, log *log.Entry, param wfv1.Paramet
 		wfUpdated = true
 	} else {
 		prevVal := wf.Status.Outputs.Parameters[index].Value
-		if prevVal == nil || *prevVal != *param.Value {
+		if prevVal == nil || (param.Value != nil && *prevVal != *param.Value) {
 			log.Infof("overwriting %s: '%s' -> '%s'", paramName, wf.Status.Outputs.Parameters[index].Value, param.Value)
 			wf.Status.Outputs.Parameters[index].Value = param.Value
 			wfUpdated = true
diff --git a/workflow/util/util_test.go b/workflow/util/util_test.go
index abfb116b3a4b..969daa48a911 100644
--- a/workflow/util/util_test.go
+++ b/workflow/util/util_test.go
@@ -322,6 +322,31 @@ func TestStopWorkflowByNodeName(t *testing.T) {
 	assert.Equal(t, wfv1.NodeFailed, wf.Status.Nodes.FindByDisplayName("approve").Phase)
 }
 
+// Regression test for #6478
+func TestAddParamToGlobalScopeValueNil(t *testing.T) {
+	paramValue := wfv1.AnyString("test")
+	wf := wfv1.Workflow{
+		Status: wfv1.WorkflowStatus{
+			Outputs: &wfv1.Outputs{
+				Parameters: []wfv1.Parameter{
+					{
+						Name:       "test",
+						Value:      &paramValue,
+						GlobalName: "global_output_param",
+					},
+				},
+			},
+		},
+	}
+
+	p := AddParamToGlobalScope(&wf, nil, wfv1.Parameter{
+		Name:       "test",
+		Value:      nil,
+		GlobalName: "test",
+	})
+	assert.False(t, p)
+}
+
 var susWorkflow = `
 apiVersion: argoproj.io/v1alpha1
 kind: Workflow