diff --git a/typed-racket-lib/typed-racket/optimizer/float-complex.rkt b/typed-racket-lib/typed-racket/optimizer/float-complex.rkt
index 0f4093b9..697e629d 100644
--- a/typed-racket-lib/typed-racket/optimizer/float-complex.rkt
+++ b/typed-racket-lib/typed-racket/optimizer/float-complex.rkt
@@ -569,8 +569,10 @@
            (log-unboxing-opt "unboxed unary float complex")
            #`(let*-values (c.bindings ...)
                ;; reuses the algorithm used by the Racket runtime
-               (let-values ([(q) (unsafe-fl/ c.real-binding c.imag-binding)])
-                 (unsafe-fl* c.imag-binding
+               (let*-values ([(r) (unsafe-flabs c.real-binding)]
+                             [(i) (unsafe-flabs c.imag-binding)]
+                             [(q) (unsafe-fl/ r i)])
+                 (unsafe-fl* i
                              (unsafe-flsqrt (unsafe-fl+ 1.0
                                                         (unsafe-fl* q q))))))])))
 
diff --git a/typed-racket-test/optimizer/known-bugs.rkt b/typed-racket-test/optimizer/known-bugs.rkt
index c04bdbf8..3181f49a 100644
--- a/typed-racket-test/optimizer/known-bugs.rkt
+++ b/typed-racket-test/optimizer/known-bugs.rkt
@@ -95,7 +95,10 @@
     (good-opt (- 0+0i 0.0+0.0i))
 
     ;; Conjugate should correctly compute sign of 0.0
-    (good-opt (conjugate 0.0+0.0i))))
+    (good-opt (conjugate 0.0+0.0i))
+
+    ;; Magnitude should always return positive results
+    (good-opt (magnitude -1.0-2i))))
 
 (module+ main
   (require rackunit/text-ui)