diff --git a/pkgs/plot-pkgs/plot-lib/plot/private/common/marching-squares.rkt b/pkgs/plot-pkgs/plot-lib/plot/private/common/marching-squares.rkt
index 09598c2826..94cba6148a 100644
--- a/pkgs/plot-pkgs/plot-lib/plot/private/common/marching-squares.rkt
+++ b/pkgs/plot-pkgs/plot-lib/plot/private/common/marching-squares.rkt
@@ -149,9 +149,7 @@ above.
 (defproc (heights->lines [xa real?] [xb real?] [ya real?] [yb real?]
                          [z real?] [z1 real?] [z2 real?] [z3 real?] [z4 real?]
                          ) (listof (list/c (vector/c real? real? real?) (vector/c real? real? real?)))
-  (cond [(and (z . < . z1) (z . < . z2) (z . < . z3) (z . < . z4))  empty]
-        [(and (z . > . z1) (z . > . z2) (z . > . z3) (z . > . z4))  empty]
-        [(= z z1 z2 z3 z4)  empty]
+  (cond [(= z z1 z2 z3 z4)  empty]
         [else
          (define lines (do-heights->lines z z1 z2 z3 z4))
          (for/list ([line  (in-list lines)])
@@ -591,8 +589,6 @@ above.
                          [z1 real?] [z2 real?] [z3 real?] [z4 real?]
                          ) (listof (listof (vector/c real? real? real?)))
   (cond
-    [(and (zb . < . z1) (zb . < . z2) (zb . < . z3) (zb . < . z4))  empty]
-    [(and (za . > . z1) (za . > . z2) (za . > . z3) (za . > . z4))  empty]
     [(= za zb z1 z2 z3 z4)  (list (list (vector xa ya z1) (vector xb ya z2)
                                         (vector xb yb z3) (vector xa yb z4)))]
     [else
diff --git a/pkgs/plot-pkgs/plot-lib/plot/private/plot2d/plot-area.rkt b/pkgs/plot-pkgs/plot-lib/plot/private/plot2d/plot-area.rkt
index 77ff41e35e..76b302ea8f 100644
--- a/pkgs/plot-pkgs/plot-lib/plot/private/plot2d/plot-area.rkt
+++ b/pkgs/plot-pkgs/plot-lib/plot/private/plot2d/plot-area.rkt
@@ -89,14 +89,15 @@
       (if identity-transforms?
           (match-lambda
             [(vector (? rational? x) (? rational? y))
-             (vector (fl (/ (- (inexact->exact x) x-min) x-size))
-                     (fl (/ (- (inexact->exact y) y-min) y-size)))]
+             (vector (fl (/ (- x x-min) x-size))
+                     (fl (/ (- y y-min) y-size)))]
             [(vector x y)
              (vector +nan.0 +nan.0)])
           (match-lambda
             [(vector (? rational? x) (? rational? y))
-             (vector (fl (/ (- (inexact->exact (fx x)) x-min) x-size))
-                     (fl (/ (- (inexact->exact (fy y)) y-min) y-size)))]
+             (let ([x  (fx x)] [y  (fy y)])
+               (vector (if (rational? x) (fl (/ (- (inexact->exact x) x-min) x-size)) +nan.0)
+                       (if (rational? y) (fl (/ (- (inexact->exact y) y-min) y-size)) +nan.0)))]
             [(vector x y)
              (vector +nan.0 +nan.0)])))
     
diff --git a/pkgs/plot-pkgs/plot-lib/plot/private/plot3d/plot-area.rkt b/pkgs/plot-pkgs/plot-lib/plot/private/plot3d/plot-area.rkt
index 2799c7c159..ed5339ddc8 100644
--- a/pkgs/plot-pkgs/plot-lib/plot/private/plot3d/plot-area.rkt
+++ b/pkgs/plot-pkgs/plot-lib/plot/private/plot3d/plot-area.rkt
@@ -152,9 +152,10 @@
              (flvector +nan.0 +nan.0 +nan.0)])
           (match-lambda
             [(vector (? rational? x) (? rational? y) (? rational? z))
-             (flvector (fl (/ (- (inexact->exact (fx x)) x-mid) x-size))
-                       (fl (/ (- (inexact->exact (fy y)) y-mid) y-size))
-                       (fl (/ (- (inexact->exact (fz z)) z-mid) z-size)))]
+             (let ([x  (fx x)] [y  (fy y)] [z  (fz z)])
+               (flvector (if (rational? x) (fl (/ (- (inexact->exact x) x-mid) x-size)) +nan.0)
+                         (if (rational? y) (fl (/ (- (inexact->exact y) y-mid) y-size)) +nan.0)
+                         (if (rational? z) (fl (/ (- (inexact->exact z) z-mid) z-size)) +nan.0)))]
             [(vector x y z)
              (flvector +nan.0 +nan.0 +nan.0)])))