diff --git a/TeXmacs/progs/graphics/graphics-markup.scm b/TeXmacs/progs/graphics/graphics-markup.scm
index e8f2645d9b..b004b16877 100644
--- a/TeXmacs/progs/graphics/graphics-markup.scm
+++ b/TeXmacs/progs/graphics/graphics-markup.scm
@@ -87,28 +87,32 @@
          (p  (if (tm-point? P) (tree->stree P) c))
          (q  (if (tm-point? Q) (tree->stree Q) p))
          (r  (points-distance c p))
-         (x  (if (equal? r 0.0)
+         (r1 (points-distance c q))
+         (x  (if (zero? r)
                 c
-                (points-add (point-times (point-get-unit (points-sub q c)) r) c)))
+                (if (zero? r1)
+                  p
+                  (points-add (point-times (point-get-unit (points-sub q c)) r) c))))
          (mid-p-x (points-mid p x))
          (vec-c-p (points-sub p c))
          (vec-c-q (points-sub q c))
-         (m  (if (equal? r 0.0)
-                c
+         (m  (if (or (zero? r) (zero? r1))
+                x
                 (if (clockwise (points-cross-product-k vec-c-p vec-c-q) 0)
                   (points-add (point-times (point-get-unit (points-sub mid-p-x c)) (- r)) c)
                   (if (= (points-cross-product-k vec-c-p vec-c-q) 0)
                     ;; If cross product == 0, then the angle between vec-c-p and vec-c-q is 0 or 180.
                     ;; We should find out whether it's 0 or 180.
+                    ;; And we should determine whether it's clockwise or counterclockwise.
                     (if (equal? (point-get-unit vec-c-p) (point-get-unit vec-c-q))
                       x
-                      (point-rotate-90 (point-rotate-90 (point-rotate-90 vec-c-p))))
+                      (if (eq? clockwise >)
+                        (points-add (point-rotate-90 (point-rotate-90 (point-rotate-90 vec-c-p))) c)
+                        (points-add (point-rotate-90 vec-c-p) c)))
                     (points-add (point-times (point-get-unit (points-sub mid-p-x c)) r) c))))))
     `(arc ,p ,m ,x)))
 
 
-
-
 (define-graphics (std-arc C P Q)
   (std-arc-helper C P Q >))
 
diff --git a/TeXmacs/tests/23_27.scm b/TeXmacs/tests/23_27.scm
new file mode 100644
index 0000000000..4a22da8a87
--- /dev/null
+++ b/TeXmacs/tests/23_27.scm
@@ -0,0 +1,78 @@
+(import (liii check)
+        (liii os))
+
+; Because std-arc-helper is using define, it is not using tm-define
+; We have to load the module directly
+;
+; (texmacs-module (tests 23_27)
+;   (:use (graphics graphics-markup)))
+(load (string-append (getenv "TEXMACS_PATH") "/progs/graphics/graphics-markup.scm"))
+
+(define (point x y)
+  (stree->tree `(point ,x ,y)))
+
+(define (test-std-arc-helper)
+  ;c==p==q
+  (check (std-arc-helper (point "0" "0") (point "0" "0") (point "0" "0") #f)
+         => `(arc (point "0" "0")
+                  (point "0" "0")
+                  (point "0" "0")))
+  ;c==p
+  (check (std-arc-helper (point "0" "0") (point "0" "0") (point "1" "1") #f)
+         => `(arc (point "0" "0")
+                  (point "0" "0")
+                  (point "0" "0")))
+  ;c==q
+  (check (std-arc-helper (point "0" "0") (point "1" "1") (point "0" "0") #f)
+         => `(arc (point "1" "1")
+                  (point "1" "1")
+                  (point "1" "1")))
+  ;p==q
+  (check (std-arc-helper (point "0" "0") (point "1" "0") (point "1" "0") >)
+         => `(arc (point "1" "0")
+                  (point "1.0" "0.0")
+                  (point "1.0" "0.0")))
+  (check (std-arc-helper (point "0" "0") (point "1" "0") (point "1" "0") <)
+         => `(arc (point "1" "0")
+                  (point "1.0" "0.0")
+                  (point "1.0" "0.0")))
+  ;cross-product==0, angle is 0 degree
+  (check (std-arc-helper (point "0" "0") (point "1" "0") (point "2" "0") >)
+         => `(arc (point "1" "0")
+                  (point "1.0" "0.0")
+                  (point "1.0" "0.0")))
+  (check (std-arc-helper (point "0" "0") (point "1" "0") (point "2" "0") <)
+         => `(arc (point "1" "0")
+                  (point "1.0" "0.0")
+                  (point "1.0" "0.0")))
+  ;cross-product==0, angle is 180 degree
+  (check (std-arc-helper (point "0" "0") (point "1" "0") (point "-2" "0") >)
+         => `(arc (point "1" "0")
+                  (point "0.0" "-1.0")
+                  (point "-1.0" "0.0")))
+  (check (std-arc-helper (point "0" "0") (point "1" "0") (point "-2" "0") <)
+         => `(arc (point "1" "0")
+                  (point "0.0" "1.0")
+                  (point "-1.0" "0.0")))
+  ;cross-product!=0
+  (check (std-arc-helper (point "0" "0") (point "1" "0") (point "0" "1") >)
+         => `(arc (point "1" "0")
+                  (point "-0.7071067811865475" "-0.7071067811865475")
+                  (point "0.0" "1.0")))
+  (check (std-arc-helper (point "0" "0") (point "1" "0") (point "0" "-1") >)
+         => `(arc (point "1" "0")
+                  (point "0.7071067811865475" "-0.7071067811865475")
+                  (point "0.0" "-1.0")))
+  (check (std-arc-helper (point "0" "0") (point "1" "0") (point "0" "1") <)
+         => `(arc (point "1" "0")
+                  (point "0.7071067811865475" "0.7071067811865475")
+                  (point "0.0" "1.0")))
+  (check (std-arc-helper (point "0" "0") (point "1" "0") (point "0" "-1") <)
+         => `(arc (point "1" "0")
+                  (point "-0.7071067811865475" "0.7071067811865475")
+                  (point "0.0" "-1.0"))))
+
+(define (test_23_27)
+  (test-std-arc-helper)
+  (check-report)
+  (if (check-failed?) (exit -1)))
\ No newline at end of file