diff --git a/opendm/boundary.py b/opendm/boundary.py
index 86ea5ae25..cc95aeb11 100644
--- a/opendm/boundary.py
+++ b/opendm/boundary.py
@@ -64,7 +64,7 @@ def load_boundary(boundary_json, reproject_to_proj4=None):
         dimensions = len(coords[0])
 
         if reproject_to_proj4 is not None:
-            t = transformer(CRS.from_proj4(fiona.crs.to_string(src.crs)),
+            t = transformer(CRS.from_user_input(src.crs),
                             CRS.from_proj4(reproject_to_proj4))
             coords = [t.TransformPoint(*c)[:dimensions] for c in coords]
         
diff --git a/tests/test_boundary.py b/tests/test_boundary.py
new file mode 100644
index 000000000..dc722017b
--- /dev/null
+++ b/tests/test_boundary.py
@@ -0,0 +1,79 @@
+import unittest
+
+from opendm.boundary import load_boundary
+
+
+class TestBoundary(unittest.TestCase):
+    def setUp(self):
+        # A simple WGS84 (EPSG:4326) GeoJSON polygon
+        self.boundary = {
+            'type': 'Feature',
+            'properties': {'name': 'boundary'},
+            'geometry': {
+                'type': 'Polygon',
+                'coordinates': [[
+                    [-91.99544, 46.84260],
+                    [-91.99417, 46.84260],
+                    [-91.99417, 46.84337],
+                    [-91.99544, 46.84337],
+                    [-91.99544, 46.84260],
+                ]]
+            }
+        }
+
+    def test_load_boundary_without_reprojection(self):
+        # Without a target CRS the coordinates are returned unchanged
+        coords = load_boundary(self.boundary)
+        self.assertEqual(len(coords), 5)
+        self.assertAlmostEqual(coords[0][0], -91.99544, places=5)
+        self.assertAlmostEqual(coords[0][1], 46.84260, places=5)
+
+    def test_load_boundary_reprojects_to_utm(self):
+        # Regression test for https://github.com/OpenDroneMap/ODM/issues/2039
+        # On fiona >= 1.10, fiona.crs.to_string() returns "EPSG:4326" instead of a
+        # PROJ4 string, which made CRS.from_proj4() raise
+        # "CRSError: Invalid PROJ string: EPSG:4326". load_boundary must reproject
+        # a WGS84 GeoJSON boundary without raising.
+        utm15n = '+proj=utm +zone=15 +datum=WGS84 +units=m +no_defs'
+        coords = load_boundary(self.boundary, utm15n)
+        self.assertEqual(len(coords), 5)
+        # Reprojected coordinates are in meters (UTM), not degrees
+        for x, y in coords:
+            self.assertGreater(abs(x), 1000)
+            self.assertGreater(abs(y), 1000)
+
+    def test_load_boundary_honors_non_wgs84_source_crs(self):
+        # GeoJSON may declare a CRS other than WGS84 (allowed by RFC 7946 and
+        # written in practice by tools like QGIS). load_boundary must reproject
+        # from the file's declared CRS, not assume EPSG:4326.
+        boundary_utm = {
+            'type': 'FeatureCollection',
+            'crs': {'type': 'name',
+                    'properties': {'name': 'urn:ogc:def:crs:EPSG::32635'}},
+            'features': [{
+                'type': 'Feature',
+                'properties': {},
+                'geometry': {
+                    'type': 'Polygon',
+                    'coordinates': [[
+                        [500000, 4540000],
+                        [501000, 4540000],
+                        [501000, 4541000],
+                        [500000, 4541000],
+                        [500000, 4540000],
+                    ]]
+                }
+            }]
+        }
+        wgs84 = '+proj=longlat +datum=WGS84 +no_defs'
+        coords = load_boundary(boundary_utm, wgs84)
+        self.assertEqual(len(coords), 5)
+        # EPSG:32635 (UTM 35N) easting 500000 / northing ~4540000 is ~27E, ~41N.
+        # If the source CRS were wrongly assumed to be WGS84, these would not land here.
+        for lon, lat in coords:
+            self.assertTrue(26 < lon < 28, "unexpected lon: %s" % lon)
+            self.assertTrue(40 < lat < 42, "unexpected lat: %s" % lat)
+
+
+if __name__ == '__main__':
+    unittest.main()