diff --git a/collects/tests/racket/number.rktl b/collects/tests/racket/number.rktl
index 18d17a021e..e769a236dc 100644
--- a/collects/tests/racket/number.rktl
+++ b/collects/tests/racket/number.rktl
@@ -1992,6 +1992,29 @@
 (test 32.0+0.0i z-round (sqrt 1024.0+0.0i))
 (test 1.0+1.5e-10i sqrt 1+3e-10i)
 
+(let* ([+pi (atan 0.0 -1.0)]
+       [-pi (- +pi)])
+  (for ([a (list (list +0.0 -0.0 +pi)
+                 (list +0.0 +0.0 +0.0)
+                 (list -0.0 -0.0 -pi)
+                 (list -0.0 +0.0 -0.0)
+                 (list +1.0 +0.0 (/ +pi 2))
+                 (list +1.0 -0.0 (/ +pi 2))
+                 (list -1.0 +0.0 (/ -pi 2))
+                 (list -1.0 -0.0 (/ -pi 2))
+                 (list +1.0 -inf.0 +pi)
+                 (list -1.0 -inf.0 -pi)
+                 (list +1.0 +inf.0 +0.0)
+                 (list -1.0 +inf.0 -0.0)
+                 (list +inf.0 1.0 (/ +pi 2))
+                 (list -inf.0 1.0 (/ -pi 2))
+                 (list +inf.0 -inf.0 (* 3/4 +pi))
+                 (list -inf.0 -inf.0 (* 3/4 -pi))
+                 (list +inf.0 +inf.0 (* 1/4 +pi))
+                 (list -inf.0 +inf.0 (* 1/4 -pi)))])
+    (test (caddr a) atan (car a) (cadr a))
+    (test (real->single-flonum (caddr a)) atan (real->single-flonum (car a)) (real->single-flonum (cadr a)))))
+
 (test 1 exp 0)
 (test 1.0 exp 0.0)
 (test 1.0 exp -0.0)
diff --git a/src/racket/src/number.c b/src/racket/src/number.c
index d979495ddf..e39616ad9f 100644
--- a/src/racket/src/number.c
+++ b/src/racket/src/number.c
@@ -2330,12 +2330,27 @@ atan_prim (int argc, Scheme_Object *argv[])
       ESCAPED_BEFORE_HERE;
     }
 
-    if ((v == 0.0) && (v2 == 0.0)) {
+    /* Handle special zero cases, just in case: */
 #ifdef MZ_USE_SINGLE_FLOATS
-      if (MZ_USE_SINGLE)
-	return scheme_zerof;
-#endif      
-      return scheme_zerod;
+# define SELECT_ATAN_PRECISION(d, s) if (MZ_USE_SINGLE) return s; return d;
+#else
+# define SELECT_ATAN_PRECISION(d, s) return d;
+#endif
+    if ((v == 0.0) && (v2 == 0.0)) {
+      if (minus_zero_p(v)) {
+        if (minus_zero_p(v2)) {
+          SELECT_ATAN_PRECISION(scheme_make_double(-SCHEME_DBL_VAL(scheme_pi)),
+                                scheme_make_float(-SCHEME_FLT_VAL(scheme_single_pi)));
+        } else {
+          SELECT_ATAN_PRECISION(scheme_nzerod, scheme_nzerof);
+        }
+      } else {
+        if (minus_zero_p(v2)) {
+          SELECT_ATAN_PRECISION(scheme_pi, scheme_single_pi);
+        } else {
+          SELECT_ATAN_PRECISION(scheme_zerod, scheme_zerof);
+        }
+      }
     }
 
 #ifdef ATAN2_DOESNT_WORK_WITH_INFINITIES
@@ -2344,6 +2359,7 @@ atan_prim (int argc, Scheme_Object *argv[])
       v2 = MZ_IS_POS_INFINITY(v2) ? 1.0 : -1.0;
     }
 #endif
+
 #ifdef ATAN2_DOESNT_WORK_WITH_NAN
     if (MZ_IS_NAN(v) || MZ_IS_NAN(v2))
       return scheme_nan_object;