diff --git a/src/nvim/diff.c b/src/nvim/diff.c
index 6dbebd5e29..19751cb73a 100644
--- a/src/nvim/diff.c
+++ b/src/nvim/diff.c
@@ -2165,6 +2165,8 @@ int diffopt_changed(void)
       } else if (STRNCMP(p, "histogram", 9) == 0) {
         p += 9;
         diff_algorithm_new = XDF_HISTOGRAM_DIFF;
+      } else {
+        return FAIL;
       }
     }