diff --git a/src/borg/helpers/parseformat.py b/src/borg/helpers/parseformat.py
index 9dfda8d24e4..d96637b4d47 100644
--- a/src/borg/helpers/parseformat.py
+++ b/src/borg/helpers/parseformat.py
@@ -95,10 +95,16 @@ def interval(s):
 
 
 def ChunkerParams(s):
+    def reject_or_warn(msg, reject):
+        if reject:
+            raise argparse.ArgumentTypeError(msg)
+        else:
+            logger.warning(msg)
+
     params = s.strip().split(',')
     count = len(params)
     if count == 0:
-        raise argparse.ArgumentTypeError('no chunker params given')
+        reject_or_warn('no chunker params given', True)
     algo = params[0].lower()
     if algo == CH_FIXED and 2 <= count <= 3:  # fixed, block_size[, header_size]
         block_size = int(params[1])
@@ -109,11 +115,9 @@ def ChunkerParams(s):
             # or in-memory chunk management.
             # choose the block (chunk) size wisely: if you have a lot of data and you cut
             # it into very small chunks, you are asking for trouble!
-            raise argparse.ArgumentTypeError('block_size must not be less than 64 Bytes')
+            reject_or_warn('block_size must not be less than 64 Bytes', False)
         if block_size > MAX_DATA_SIZE or header_size > MAX_DATA_SIZE:
-            raise argparse.ArgumentTypeError(
-                'block_size and header_size must not exceed MAX_DATA_SIZE [%d]' % MAX_DATA_SIZE
-            )
+            reject_or_warn('block_size and header_size must not exceed MAX_DATA_SIZE [%d]' % MAX_DATA_SIZE, True)
         return algo, block_size, header_size
     if algo == 'default' and count == 1:  # default
         return CHUNKER_PARAMS
@@ -121,16 +125,12 @@ def ChunkerParams(s):
     if algo == CH_BUZHASH and count == 5 or count == 4:  # [buzhash, ]chunk_min, chunk_max, chunk_mask, window_size
         chunk_min, chunk_max, chunk_mask, window_size = (int(p) for p in params[count - 4:])
         if not (chunk_min <= chunk_mask <= chunk_max):
-            raise argparse.ArgumentTypeError('required: chunk_min <= chunk_mask <= chunk_max')
+            reject_or_warn('required: chunk_min <= chunk_mask <= chunk_max', False)
         if chunk_min < 6:
             # see comment in 'fixed' algo check
-            raise argparse.ArgumentTypeError(
-                'min. chunk size exponent must not be less than 6 (2^6 = 64B min. chunk size)'
-            )
+            reject_or_warn('min. chunk size exponent must not be less than 6 (2^6 = 64B min. chunk size)', False)
         if chunk_max > 23:
-            raise argparse.ArgumentTypeError(
-                'max. chunk size exponent must not be more than 23 (2^23 = 8MiB max. chunk size)'
-            )
+            reject_or_warn('max. chunk size exponent must not be more than 23 (2^23 = 8MiB max. chunk size)', True)
         return CH_BUZHASH, chunk_min, chunk_max, chunk_mask, window_size
     raise argparse.ArgumentTypeError('invalid chunker params')
 
diff --git a/src/borg/testsuite/helpers.py b/src/borg/testsuite/helpers.py
index 99057a3d290..ed7140e5aeb 100644
--- a/src/borg/testsuite/helpers.py
+++ b/src/borg/testsuite/helpers.py
@@ -349,16 +349,20 @@ def test_chunkerparams():
     assert ChunkerParams('fixed,4096') == ('fixed', 4096, 0)
     assert ChunkerParams('fixed,4096,200') == ('fixed', 4096, 200)
     # invalid values checking
+    borg2 = False  # for borg < 2, we only emit a warning, but do not raise ArgumentTypeError for some cases
     with pytest.raises(ArgumentTypeError):
         ChunkerParams('crap,1,2,3,4')  # invalid algo
-    with pytest.raises(ArgumentTypeError):
-        ChunkerParams('buzhash,5,7,6,4095')  # too small min. size
+    if borg2:
+        with pytest.raises(ArgumentTypeError):
+            ChunkerParams('buzhash,5,7,6,4095')  # too small min. size
     with pytest.raises(ArgumentTypeError):
         ChunkerParams('buzhash,19,24,21,4095')  # too big max. size
-    with pytest.raises(ArgumentTypeError):
-        ChunkerParams('buzhash,23,19,21,4095')  # violates min <= mask <= max
-    with pytest.raises(ArgumentTypeError):
-        ChunkerParams('fixed,63')  # too small block size
+    if borg2:
+        with pytest.raises(ArgumentTypeError):
+            ChunkerParams('buzhash,23,19,21,4095')  # violates min <= mask <= max
+    if borg2:
+        with pytest.raises(ArgumentTypeError):
+            ChunkerParams('fixed,63')  # too small block size
     with pytest.raises(ArgumentTypeError):
         ChunkerParams('fixed,%d,%d' % (MAX_DATA_SIZE + 1, 4096))  # too big block size
     with pytest.raises(ArgumentTypeError):