NASA and SpaceX have delayed the launch of a Cargo Dragon spacecraft for at least a couple of weeks due to an issue during the prelaunch loading of hypergolic propellants.

The space agency had been planning to launch the spacecraft on June 12 but announced the delay in an email on Monday evening to reporters.

“During propellant loading of the Cargo Dragon spacecraft, elevated vapor readings of mono-methyl hydrazine were measured in an isolated region of the Draco thruster propulsion system,” the space agency’s statement said. “The propellant and oxidizer have been offloaded from that region to support further inspections and testing.”