Never has the phrase "Keep calm and carry on" been so apropos. Buckingham Palace guards are famously stoic, even in the face of great distraction, but one gentleman inadvertently (and very literally) fell out of line during a recent Changing of the Guard ceremony.

As seen in the above video from SWNS TV, posted to YouTube on April 14, the Household Troops were going about their daily ceremonial duties when one of them slipped on what appears to be a manhole cover. After a brief moment of flailing, he slid sideways and hit the ground, dropping his rifle in the process.

Ever the professional, he quickly returned to his feet and resumed position, suppressing a slight smile as his colleagues continued, stone-faced, through their routine.

According to the website of the Royal Collection Trust, Changing of the Guard occurs at Buckingham Palace every day at 11:30 a.m. from April through July (and on alternate days the rest of the year).

Watch the video above!