diff --git a/source/blender/modifiers/intern/MOD_grease_pencil_opacity.cc b/source/blender/modifiers/intern/MOD_grease_pencil_opacity.cc
index 2879d271c5d..de75b7f661a 100644
--- a/source/blender/modifiers/intern/MOD_grease_pencil_opacity.cc
+++ b/source/blender/modifiers/intern/MOD_grease_pencil_opacity.cc
@@ -161,10 +161,10 @@ static void modify_hardness(const GreasePencilOpacityModifierData &omd,
                             const IndexMask &curves_mask)
 {
   bke::MutableAttributeAccessor attributes = curves.attributes_for_write();
-  bke::SpanAttributeWriter<float> hardnesses = attributes.lookup_for_write_span<float>("hardness");
-  if (!hardnesses) {
-    return;
-  }
+  bke::SpanAttributeWriter<float> hardnesses = attributes.lookup_or_add_for_write_span<float>(
+      "hardness",
+      bke::AttrDomain::Curve,
+      bke::AttributeInitVArray(VArray<float>::ForSingle(1.0f, curves.curve_num)));
 
   curves_mask.foreach_index(GrainSize(512), [&](int64_t curve_i) {
     hardnesses.span[curve_i] = std::clamp(