From 936 to 937 he led an expedition against the Muslims. As a result of this successful campaign many of the enemy forces were killed, including the Qadi of Valencia. The Moors temporarily abandoned Tarragona (which became a no-man's land), while Tortosa was forced to pay a tribute to the count. This gain was short-lived however, as Abd ar-Rahman III sent envoys and a fleet to Barcelona in 940, forcing Sunyer into a subservient alliance and to abandon a marriage pact he had reached with king García Sánchez I of Pamplona, who was to marry (or had already married) Sunyer's daughter.