diff --git a/sketch_map_tool/helpers.py b/sketch_map_tool/helpers.py
index 74bb8185..d2925824 100644
--- a/sketch_map_tool/helpers.py
+++ b/sketch_map_tool/helpers.py
@@ -1,8 +1,10 @@
+from io import BytesIO
 from pathlib import Path
 
 import cv2
 import numpy as np
 from numpy.typing import NDArray
+from PIL import Image as PILImage
 from reportlab.graphics.shapes import Drawing
 
 
@@ -27,3 +29,18 @@ def resize_rlg_by_height(d: Drawing, size: float) -> Drawing:
 
 def to_array(buffer: bytes) -> NDArray:
     return cv2.imdecode(np.fromstring(buffer, dtype="uint8"), cv2.IMREAD_UNCHANGED)
+
+
+def resize_png(input_buffer: BytesIO, max_length: float) -> BytesIO:
+    input_img = PILImage.open(input_buffer)
+    ratio = input_img.width / input_img.height
+    if ratio > 1:
+        width = min(max_length, input_img.width)
+        height = width / ratio
+    else:
+        height = min(max_length, input_img.height)
+        width = height * ratio
+    output_image = BytesIO()
+    input_img.resize((int(width), int(height))).save(output_image, format="png")
+    output_image.seek(0)
+    return output_image
diff --git a/sketch_map_tool/map_generation/generate_pdf.py b/sketch_map_tool/map_generation/generate_pdf.py
index a9b1ff64..6330d9e0 100644
--- a/sketch_map_tool/map_generation/generate_pdf.py
+++ b/sketch_map_tool/map_generation/generate_pdf.py
@@ -18,7 +18,7 @@
 from svglib.svglib import svg2rlg
 
 from sketch_map_tool.definitions import PDF_RESOURCES_PATH
-from sketch_map_tool.helpers import resize_rlg_by_width
+from sketch_map_tool.helpers import resize_png, resize_rlg_by_width
 from sketch_map_tool.models import PaperFormat
 
 # PIL should be able to open high resolution PNGs of large Maps:
@@ -26,7 +26,7 @@
 
 
 def generate_pdf(  # noqa: C901
-    map_image_input: PILImage,
+    map_frame_input: PILImage,
     qr_code: Drawing,
     format_: PaperFormat,
     scale: float,
@@ -38,13 +38,13 @@ def generate_pdf(  # noqa: C901
 
     Also generate template image (PNG) as Pillow object for later upload processing
 
-    :param map_image_input: Image of the map to be used as sketch map.
+    :param map_frame_input: Image of the map to be used as sketch map.
     :param qr_code: QR code to be included on the sketch map for georeferencing.
     :param format_: Paper format of the PDF document.
     :param scale: Ratio for the scale in the sketch map legend
     :return: Sketch Map PDF, Template image
     """
-    map_width_px, map_height_px = map_image_input.size
+    map_width_px, map_height_px = map_frame_input.size
     map_margin = format_.map_margin
 
     # TODO: Use orientation parameter to determine rotation
@@ -68,14 +68,14 @@ def generate_pdf(  # noqa: C901
     column_origin_y = 0
     column_margin = map_margin * cm
 
-    map_image_reportlab = PIL_image_to_image_reader(map_image_input)
+    map_frame_reportlab = PIL_image_to_image_reader(map_frame_input)
 
     # calculate m per px in map frame
     cm_per_px = frame_width * scale / map_width_px
     m_per_px = cm_per_px / 100
     # create map_image by adding globes
-    map_img = create_map_frame(
-        map_image_reportlab, format_, map_height_px, map_width_px, portrait, m_per_px
+    map_frame = create_map_frame(
+        map_frame_reportlab, format_, map_height_px, map_width_px, portrait, m_per_px
     )
 
     map_pdf = BytesIO()
@@ -85,7 +85,7 @@ def generate_pdf(  # noqa: C901
     # Add map to canvas:
     canv_map_margin = map_margin
     canv_map.drawImage(
-        ImageReader(map_img),
+        ImageReader(map_frame),
         canv_map_margin * cm,
         canv_map_margin * cm,
         mask="auto",
@@ -123,16 +123,13 @@ def generate_pdf(  # noqa: C901
     canv_map.save()
 
     map_pdf.seek(0)
-    map_img.seek(0)
+    map_frame.seek(0)
 
-    if portrait:  # Rotate the map frame for correct georeferencing
-        map_img_rotated_bytes = BytesIO()
-        map_img_rotated = PILImage.open(map_img).rotate(270, expand=1)
-        map_img_rotated.save(map_img_rotated_bytes, format="png")
-        map_img_rotated_bytes.seek(0)
-        map_img = map_img_rotated_bytes
+    # Resize map_frame if a length of 2000 px is exceeded in one dimension to avoid very large objects in upload
+    # processing of e.g. A0 maps
+    map_frame = resize_png(map_frame, max_length=2000)
 
-    return map_pdf, map_img
+    return map_pdf, map_frame
 
 
 def draw_right_column(
diff --git a/sketch_map_tool/tasks.py b/sketch_map_tool/tasks.py
index 180f9d16..101b76a2 100644
--- a/sketch_map_tool/tasks.py
+++ b/sketch_map_tool/tasks.py
@@ -54,19 +54,19 @@ def generate_sketch_map(
 ) -> BytesIO | AsyncResult:
     """Generate and returns a sketch map as PDF and stores the map frame in DB."""
     raw = wms_client.get_map_image(bbox, size)
-    map_image = wms_client.as_image(raw)
+    map_frame = wms_client.as_image(raw)
     qr_code_ = map_generation.qr_code(
         str(uuid),
         bbox,
         format_,
     )
-    map_pdf, map_img = map_generation.generate_pdf(
-        map_image,
+    map_pdf, map_frame = map_generation.generate_pdf(
+        map_frame,
         qr_code_,
         format_,
         scale,
     )
-    db_client_celery.insert_map_frame(map_img, uuid)
+    db_client_celery.insert_map_frame(map_frame, uuid)
     return map_pdf
 
 
diff --git a/tests/fixtures/map-img-big-landscape.jpg b/tests/fixtures/map-img-big-landscape.jpg
new file mode 100644
index 00000000..2caefe2c
Binary files /dev/null and b/tests/fixtures/map-img-big-landscape.jpg differ
diff --git a/tests/fixtures/map-img-big-portrait.jpg b/tests/fixtures/map-img-big-portrait.jpg
new file mode 100644
index 00000000..cdad0df2
Binary files /dev/null and b/tests/fixtures/map-img-big-portrait.jpg differ
diff --git a/tests/unit/test_helpers.py b/tests/unit/test_helpers.py
index f0beb73d..bea4e40c 100644
--- a/tests/unit/test_helpers.py
+++ b/tests/unit/test_helpers.py
@@ -1,5 +1,9 @@
+from io import BytesIO
 from pathlib import Path
 
+import pytest
+from PIL import Image
+
 from sketch_map_tool import helpers
 
 
@@ -7,3 +11,41 @@ def test_get_project_root():
     expected = Path(__file__).resolve().parent.parent.parent.resolve()
     result = helpers.get_project_root()
     assert expected == result
+
+
+@pytest.mark.parametrize(
+    ("max_length", "width_exp", "height_exp"),
+    [
+        (1450, 1450, 1232),  # One dimension too big
+        (1000, 1000, 850),  # Both dimensions too big
+        (1456, 1456, 1238),  # Not too big, exactly limit
+        (1600, 1456, 1238),  # Not too big, smaller than limit
+    ],
+)
+def test_resize_png(map_frame_buffer, max_length, width_exp, height_exp):
+    img = Image.open(map_frame_buffer)
+    img_rotated = img.rotate(90, expand=1)
+    width, height = img.width, img.height
+    width_rotated, height_rotated = img_rotated.width, img_rotated.height
+    assert width == 1456 and height == 1238
+    assert width_rotated == 1238 and height_rotated == 1456
+
+    img_rotated_buffer = BytesIO()
+    img_rotated.save(img_rotated_buffer, format="png")
+    img_rotated_buffer.seek(0)
+
+    img_resized_buffer = helpers.resize_png(map_frame_buffer, max_length=max_length)
+    img_rotated_resized_buffer = helpers.resize_png(
+        img_rotated_buffer, max_length=max_length
+    )
+    img_resized = Image.open(img_resized_buffer)
+    img_rotated_resized = Image.open(img_rotated_resized_buffer)
+
+    width_resized, height_resized = img_resized.width, img_resized.height
+    width_rotated_resized, height_rotated_resized = (
+        img_rotated_resized.width,
+        img_rotated_resized.height,
+    )
+
+    assert width_resized == width_exp and height_resized == height_exp
+    assert width_rotated_resized == height_exp and height_rotated_resized == width_exp
diff --git a/tests/unit/test_map_generation.py b/tests/unit/test_map_generation.py
index cb664c2b..0592904e 100644
--- a/tests/unit/test_map_generation.py
+++ b/tests/unit/test_map_generation.py
@@ -55,6 +55,14 @@ def map_image(request):
     return Image.open(p)
 
 
+@pytest.fixture
+def map_image_too_big(request):
+    """Map image from WMS exceeding the limit on map frame size"""
+    orientation = request.getfixturevalue("orientation")
+    p = FIXTURE_DIR / "map-img-big-{}.jpg".format(orientation)
+    return Image.open(p)
+
+
 @pytest.fixture
 def qr_code(bbox, format_, size):
     return generate_qr_code(
@@ -109,6 +117,25 @@ def test_generate_pdf(
     # )
 
 
+@pytest.mark.parametrize("orientation", ["landscape", "portrait"])
+def test_generate_pdf_map_frame_too_big(
+    map_image_too_big,
+    qr_code,
+    orientation,
+) -> None:
+    sketch_map, sketch_map_template = generate_pdf(
+        map_image_too_big,
+        qr_code,
+        A0,
+        1283.129,
+    )
+
+    map_frame_img = Image.open(sketch_map_template)
+
+    # Check that the upper limit on map frame size is enforced
+    assert map_frame_img.width <= 2000 and map_frame_img.height <= 2000
+
+
 def test_get_globes(format_):
     globes = get_globes(format_.globe_scale)
     for globe in globes: