A surgical anvil assembly for use with a circular stapling instrument, comprising: an anvil center rod; an anvil head pivotally coupled to the anvil center rod and movable between a first, operative condition and a second, tilted condition; and a backup member slidably disposed within a recess of the anvil head and selectively engagable with the anvil center rod; characterised in that the surgical anvil assembly further comprises a locking assembly including: an inner member supported on a distally-facing outer surface of the anvil head; an outer member movably coupled to the inner member; and a post interconnecting the outer member and the backup member, wherein the outer member is configured to move relative to the inner member between a first, proximal position, in which the locking assembly maintains the backup member engaged with the anvil center rod to resist movement of the anvil head relative to the anvil center rod, and a second, distal position, in which the locking assembly maintains the backup member disengaged from the anvil center rod to allow for movement of the anvil head relative to the anvil center rod, wherein the locking assembly further includes at least one locking member (106a, 106b) protruding outwardly from the inner member, the at least one locking member configured to engage the outer member when the outer member is in the second, distal position to maintain the outer member in the second, distal position and, in turn, maintain the backup member disengaged from the anvil center rod, wherein the at least one locking member is configured to prevent movement of the backup member from the first, proximal position toward the second, distal position until a threshold, distally-oriented force has been applied to the backup member. an anvil center rod; an anvil head pivotally coupled to the anvil center rod and movable between a first, operative condition and a second, tilted condition; and a backup member slidably disposed within a recess of the anvil head and selectively engagable with the anvil center rod; characterised in that the surgical anvil assembly further comprises a locking assembly including: an inner member supported on a distally-facing outer surface of the anvil head; an outer member movably coupled to the inner member; and a post interconnecting the outer member and the backup member, wherein the outer member is configured to move relative to the inner member between a first, proximal position, in which the locking assembly maintains the backup member engaged with the anvil center rod to resist movement of the anvil head relative to the anvil center rod, and a second, distal position, in which the locking assembly maintains the backup member disengaged from the anvil center rod to allow for movement of the anvil head relative to the anvil center rod, wherein the locking assembly further includes at least one locking member (106a, 106b) protruding outwardly from the inner member, the at least one locking member configured to engage the outer member when the outer member is in the second, distal position to maintain the outer member in the second, distal position and, in turn, maintain the backup member disengaged from the anvil center rod, wherein the at least one locking member is configured to prevent movement of the backup member from the first, proximal position toward the second, distal position until a threshold, distally-oriented force has been applied to the backup member. an inner member supported on a distally-facing outer surface of the anvil head; an outer member movably coupled to the inner member; and a post interconnecting the outer member and the backup member, wherein the outer member is configured to move relative to the inner member between a first, proximal position, in which the locking assembly maintains the backup member engaged with the anvil center rod to resist movement of the anvil head relative to the anvil center rod, and a second, distal position, in which the locking assembly maintains the backup member disengaged from the anvil center rod to allow for movement of the anvil head relative to the anvil center rod, wherein the locking assembly further includes at least one locking member (106a, 106b) protruding outwardly from the inner member, the at least one locking member configured to engage the outer member when the outer member is in the second, distal position to maintain the outer member in the second, distal position and, in turn, maintain the backup member disengaged from the anvil center rod, wherein the at least one locking member is configured to prevent movement of the backup member from the first, proximal position toward the second, distal position until a threshold, distally-oriented force has been applied to the backup member.