What is a substantial modification?
Under Article 3(16), a substantial modification is a physical or digital modification made after a machine or related product has been placed on the market or put into service, which the original manufacturer did not foresee or plan. It affects safety by creating a new hazard or increasing an existing risk. The definition also requires certain additional protective measures: additional guards or protective devices whose integration requires adaptation of the existing safety control system, or additional measures to ensure stability or mechanical strength. The conditions must be considered together in the particular case.
Physical modifications
New mechanical components, additional axes, a changed safety control system, changes to stability or substantial performance changes may call for an assessment. These examples are not automatically substantial modifications. A repair or modernisation does not automatically meet the statutory conditions either.
Digital modifications
The definition expressly includes digital modifications. A substantial change to control software, new safety-related software functions, autonomous functions, retrofitted AI or changes to safety logic may require specialist consideration. An ordinary software update is not substantial for that reason alone.
Who may be affected?
Machine operators, retrofit companies, system integrators, automation specialists, machinery manufacturers and businesses with their own maintenance function. Even a person who did not originally build the machine may assume manufacturer obligations because of their activity.
What may be the consequence?
Where a substantial modification exists, Article 18 treats the modifying person as the manufacturer for the affected machinery or related product and subjects that person to the manufacturer obligations in Article 10. For an assembly of machinery, this may, subject to the risk assessment, be limited to the affected machinery or related product. The consequences can include a risk assessment, technical documentation, the applicable conformity assessment procedure and a declaration of conformity under the person’s own responsibility. Article 18 contains an exception for non-professional users modifying machinery for their own use.
Example: a welding installation is modernised
A system integrator adds a new control system, sensors, safety functions and autonomous software. The company and its competent specialists determine whether the conditions for a substantial modification are met. The product dossier links the initial state with the modification description, risk records and the newly documented machine state.
Document rather than classify automatically
Default status: classification by the company required. Companies can document their classification or an external assessment. Roboterausweis does not generate an automatic yes/no outcome from individual answers. Earlier records, software states and declarations of conformity are not overwritten.
Official sources
Source status: 10 October 2026. General information; not a legal assessment of any individual case.
EUR-Lex · EU Machinery Regulation (opens in a new window)