diff --git a/math-lib/math/private/matrix/matrix-basic.rkt b/math-lib/math/private/matrix/matrix-basic.rkt
index f22538a..cc024b9 100644
--- a/math-lib/math/private/matrix/matrix-basic.rkt
+++ b/math-lib/math/private/matrix/matrix-basic.rkt
@@ -355,7 +355,10 @@
      
          (inner A* B*)]
         [(or (nan? mxA) (nan? mxB) (= 0 mxA) (= 0 mxB))
-         (/ (matrix-dot A B) (* mxA mxB))]
+         (cond
+           [(eqv? mxA 0) (error 'matrix-cos-angle "zero matrix ~a" A)]
+           [(eqv? mxB 0) (error 'matrix-cos-angle "zero matrix ~a" B)]
+           [else         (/ (matrix-dot A B) (* mxA mxB))])]
         [else
          (define A* (if (rational? mxA)
                         (inline-array-map (λ (x) (/ x mxA)) A)
diff --git a/math-test/math/tests/matrix-tests.rkt b/math-test/math/tests/matrix-tests.rkt
index 076cf6d..bbb92aa 100644
--- a/math-test/math/tests/matrix-tests.rkt
+++ b/math-test/math/tests/matrix-tests.rkt
@@ -686,8 +686,11 @@
 (for: ([i (in-range 10)])
       (define n (+ 1 (random 3)))
       (define m (+ 1 (random 4)))
-      (define A (random-matrix n m))
-      (define B (random-matrix n m))
+      (define (non-zero-random-matrix [n : Integer] [m : Integer]) : (Array Integer)
+        (define A (random-matrix n m))
+        (if (matrix-zero? A) (non-zero-random-matrix n m) A))
+      (define A (non-zero-random-matrix n m))
+      (define B (non-zero-random-matrix n m))
       (define ca (matrix-cos-angle A B))
       (check-true (or (and (rational? ca) (<= ca 1.))
                       (matrix-zero? A) (matrix-zero? B))))
@@ -714,6 +717,8 @@
                                 (matrix [[3 -8+inf.0i]]))
               (matrix-cos-angle (matrix [[2 9]])
                                 (matrix [[0. -0+1.0i]])))
+(check-exn #px"matrix-cos-angle: zero matrix " (λ () (matrix-cos-angle (matrix [[0 0][0 0]]) (matrix [[3 1][-1 2]]))))
+(check-exn #px"matrix-cos-angle: zero matrix " (λ () (matrix-angle (matrix [[1]]) (matrix [[0]]))))
 
 ;; TODO: matrix-normalize