diff --git a/mats/5_3.ms b/mats/5_3.ms
index 29f1a16305..1f2dd79cc7 100644
--- a/mats/5_3.ms
+++ b/mats/5_3.ms
@@ -2816,6 +2816,10 @@
     (let ([x 0.5+1.5i]) (cfl~= (asin (sin x)) x))
     (let ([x 0.5-1.5i]) (cfl~= (asin (sin x)) x))
     (let ([z 2.2-1.1i]) (cfl~= (asin z) (/ (asinh (* +1.0i z)) +1.0i)))
+    (fl~= 1.5707963267948966 (real-part (asin +inf.0)))
+    (eqv? -inf.0 (imag-part (asin +inf.0)))
+    (fl~= -1.5707963267948966 (real-part (asin -inf.0)))
+    (eqv? +inf.0 (imag-part (asin -inf.0)))
  )
 
 (mat acos
@@ -2834,6 +2838,8 @@
                              (* +1.0i (sqrt (/ (- 1 z) 2))))))
                 +1.0i)))
     (let ([x 10+10.0i]) (cfl~= (+ (asin x) (acos x)) (/ pi 2)))
+    (fl~= 1.5707963267948966 (real-part (acos -inf.0i)))
+    (eqv? +inf.0 (imag-part (acos -inf.0i)))
  )
 
 (mat atan
diff --git a/s/5_3.ss b/s/5_3.ss
index ee253bb158..da5a07fbf5 100644
--- a/s/5_3.ss
+++ b/s/5_3.ss
@@ -468,7 +468,7 @@
             [z+ (cflsqrt (cfl+ 1.0 z))])
          (let ([a (cfl-real-part z-)] [b (cfl-imag-part z-)]
                [c (cfl-real-part z+)] [d (cfl-imag-part z+)])
-            (fl-make-rectangular (fl* 2.0 ($flatan (fl/ a c)))
+            (fl-make-rectangular (fl* 2.0 (flatan2 a c))
                                  (flasinh (fl- (fl* b c) (fl* a d))))))))
 
 (define cflasin
@@ -484,7 +484,9 @@
          (let ([a (cfl-real-part z-)] [b (cfl-imag-part z-)]
                [c (cfl-real-part z+)] [d (cfl-imag-part z+)])
             (fl-make-rectangular
-               ($flatan (fl/ (cfl-real-part z) (fl- (fl* a c) (fl* b d))))
+               (flatan2 (cfl-real-part z) (if (flonum? z)
+                                              0.0
+                                              (fl- (fl* a c) (fl* b d))))
                (flasinh (fl- (fl* a d) (fl* b c))))))))
 
 (define cflasinh