patch 8.1.0513: no error for set diffopt+=algorithm: commit https://github.com/vim/vim/commit/d0721058f494143186f66a60151c9634031a8c96 Author: Bram Moolenaar <Bram@vim.org> Date: Mon Nov 5 21:21:33 2018 +0100 patch 8.1.0513: no error for set diffopt+=algorithm: Problem: No error for set diffopt+=algorithm:. Solution: Check for missing argument. (Hirohito Higashi, closes https://github.com/vim/vim/issues/3598)

--- a/src/diff.c
+++ b/src/diff.c
@@ -2266,6 +2266,8 @@ diffopt_changed(void)
 		p += 9;
 		diff_algorithm_new = XDF_HISTOGRAM_DIFF;
 	    }
+	    else
+		return FAIL;
 	}
 
 	if (*p != ',' && *p != NUL)