diff --git a/libs/gfx/include/psemek/gfx/gltf_animation.hpp b/libs/gfx/include/psemek/gfx/gltf_animation.hpp
index 22514385..891ce752 100644
--- a/libs/gfx/include/psemek/gfx/gltf_animation.hpp
+++ b/libs/gfx/include/psemek/gfx/gltf_animation.hpp
@@ -30,6 +30,11 @@ namespace psemek::gfx
 			{
 				return geom::lerp(v1, v2, t);
 			}
+
+			static output_type normalize(output_type const & v)
+			{
+				return v;
+			}
 		};
 
 		template <>
@@ -46,6 +51,11 @@ namespace psemek::gfx
 			{
 				return geom::slerp(v1, v2, t);
 			}
+
+			static output_type normalize(output_type const & v)
+			{
+				return geom::normalized(v);
+			}
 		};
 
 		template <>
@@ -62,6 +72,11 @@ namespace psemek::gfx
 			{
 				return geom::lerp(v1, v2, t);
 			}
+
+			static output_type normalize(output_type const & v)
+			{
+				return v;
+			}
 		};
 
 	}
@@ -116,12 +131,12 @@ namespace psemek::gfx
 					// see https://github.khronos.org/glTF-Tutorials/gltfTutorial/gltfTutorial_007_Animations.html#cubic-spline-interpolation
 					float t2 = t * t;
 					float t3 = t * t2;
-					return traits::default_value()
+					return traits::normalize(output_type::zero()
 						+ output_[3 * (i - 1) + 1] * (  2.f * t3 - 3.f * t2 + 1.f)
 						+ output_[3 * (i - 1) + 2] * (        t3 - 2.f * t2 + t  )
 						+ output_[3 * (i + 0) + 1] * (- 2.f * t3 + 3.f * t2      )
 						+ output_[3 * (i + 0) + 0] * (        t3 -       t2      )
-						;
+						);
 				}
 			default:
 				throw std::runtime_error("unsupported glTF animation interpolation type");