diff --git a/test/unit/projection/proj_transform.cpp b/test/unit/projection/proj_transform.cpp
index 5fc30459b..31fc2f1ea 100644
--- a/test/unit/projection/proj_transform.cpp
+++ b/test/unit/projection/proj_transform.cpp
@@ -128,9 +128,20 @@ SECTION("Test proj antimeridian bbox")
     mapnik::proj_transform prj_trans_fwd(prj_proj, prj_geog);
     mapnik::proj_transform prj_trans_rev(prj_geog, prj_proj);
 
-    // bad = mapnik.Box2d(-177.31453250437079, -62.33374815225163, 178.02778363316355, -24.584597490955804)
-    const mapnik::box2d<double> better(-180.0, -62.33374815225163,
-                                        180.0, -24.584597490955804);
+    // reference values taken from proj4 command line tool:
+    // (non-corner points assume PROJ_ENVELOPE_POINTS == 20)
+    //
+    //  cs2cs -Ef %.10f +init=epsg:2193 +to +init=epsg:4326 <<END
+    //        2105800 3087000 # left-most
+    //        1495200 3087000 # bottom-most
+    //        2105800 7173000 # right-most
+    //        3327000 7173000 # top-most
+    //  END
+    //
+    // wrong = mapnik.Box2d(-177.3145325044, -62.3337481525,
+    //                       178.0277836332, -24.5845974912)
+    const mapnik::box2d<double> better(-180.0, -62.3337481525,
+                                        180.0, -24.5845974912);
 
     {
         mapnik::box2d<double> ext(274000, 3087000, 3327000, 7173000);
@@ -151,18 +162,17 @@ SECTION("Test proj antimeridian bbox")
         CHECK(ext.maxy() == Approx(better.maxy()));
     }
 
-    {
-        // checks for not being snapped (ie. not antimeridian)
-        mapnik::box2d<double> ext(274000, 3087000, 3327000, 7173000);
-        prj_trans_rev.backward(ext, PROJ_ENVELOPE_POINTS);
-        CHECK(ext.minx() == Approx(better.minx()));
-        CHECK(ext.miny() == Approx(better.miny()));
-        CHECK(ext.maxx() == Approx(better.maxx()));
-        CHECK(ext.maxy() == Approx(better.maxy()));
-    }
-
-    const mapnik::box2d<double> normal(148.766759749, -60.1222810238,
-                                       159.95484893, -24.9774643167);
+    // reference values taken from proj4 command line tool:
+    //
+    //  cs2cs -Ef %.10f +init=epsg:2193 +to +init=epsg:4326 <<END
+    //        274000 3087000 # left-most
+    //        276000 3087000 # bottom-most
+    //        276000 7173000 # right-most
+    //        274000 7173000 # top-most
+    //  END
+    //
+    const mapnik::box2d<double> normal(148.7667597489, -60.1222810241,
+                                       159.9548489296, -24.9771195155);
 
     {
         // checks for not being snapped (ie. not antimeridian)