diff --git a/dali/python/nvidia/dali/external_source.py b/dali/python/nvidia/dali/external_source.py
index 67d9a41a003..85ca7dccb3f 100644
--- a/dali/python/nvidia/dali/external_source.py
+++ b/dali/python/nvidia/dali/external_source.py
@@ -106,6 +106,7 @@ def call_and_feed(self, pipeline, batch_size):
         try:
             if self.batch:
                 callback_out = self.callback(*self.callback_args(None))
+                batch_size = len(callback_out[0]) if self.is_multioutput else len(callback_out)
             else:
                 callback_out = [self.callback(*self.callback_args(i)) for i in range(batch_size)]
             self.current_sample += batch_size
@@ -118,6 +119,8 @@ def call_and_feed(self, pipeline, batch_size):
             for op in self.instances:
                 if self.batch:
                     data = callback_out[op._output_index]
+                    if len(data) != batch_size:
+                        raise RuntimeError("External source returned outputs with different batch sizes.")
                 else:
                     # extract a single output
                     data = [callback_out[i][op._output_index] for i in range(batch_size)]
@@ -126,6 +129,7 @@ def call_and_feed(self, pipeline, batch_size):
             data = callback_out
             op = self.instances[0]
             pipeline.feed_input(op._name, data, op._layout, self._cuda_stream, self.use_copy_kernel)
+        return batch_size
 
 def _is_generator_function(x):
     """Checks whether x is a generator function or a callable object
diff --git a/dali/python/nvidia/dali/pipeline.py b/dali/python/nvidia/dali/pipeline.py
index 4ba5da23ed1..34a9e115cbe 100644
--- a/dali/python/nvidia/dali/pipeline.py
+++ b/dali/python/nvidia/dali/pipeline.py
@@ -465,12 +465,16 @@ def _prepare_graph(self, define_graph = None):
 
     def _setup_input_callbacks(self):
         from nvidia.dali.external_source import _is_external_source_with_callback
-        groups = set()
+        groups_batch = set()
+        groups_sample = set()
         for op in self._ops:
             if _is_external_source_with_callback(op):
                 group = op._group
-                groups.add(group)
-        self._input_callbacks = list(groups)
+                if group.batch:
+                    groups_batch.add(group)
+                else:
+                    groups_sample.add(group)
+        self._input_callbacks = list(groups_batch) + list(groups_sample)
 
     def build(self, define_graph = None):
         """Build the pipeline.
@@ -983,9 +987,16 @@ def _run_input_callbacks(self):
             return
 
         stop_iter = False
+        batch_size = self._max_batch_size
+        first = True
         for group in self._input_callbacks:
             try:
-                group.call_and_feed(self, self._max_batch_size)
+                actual_batch_size = group.call_and_feed(self, batch_size)
+                if first:
+                    batch_size = actual_batch_size
+                    first = False
+                elif actual_batch_size != batch_size:
+                    raise RuntimeError("Batch size inconsistency between ExternalSource operators")
             except StopIteration:
                 stop_iter = True
         if stop_iter:
diff --git a/dali/test/python/test_external_source_impl.py b/dali/test/python/test_external_source_impl.py
index e6d203147ff..398c44121da 100644
--- a/dali/test/python/test_external_source_impl.py
+++ b/dali/test/python/test_external_source_impl.py
@@ -22,6 +22,7 @@
 from test_utils import check_output
 import random
 from collections import Iterable
+import itertools
 datapy = np
 
 make_array = np.array
@@ -699,3 +700,26 @@ def test_iter_setup_zero_copy():
                     # make it -5 as -1 sometimes works, sometimes not due to being close to the limit
                     for additional_num_keep_samples in [-4, 0, 1]:
                         yield _test_iter_setup_zero_copy, use_fn_api, by_name, as_tensor, device, additional_num_keep_samples
+
+def test_external_source_variable_batch_size():
+    batch_data = [
+        [[1,2,3],[4,5]],
+        [[7,8,9,10],[11],[12],[13],[14]],
+        [[15,16]]
+    ]
+    batch_data = [[np.array(x) for x in b] for b in batch_data]
+    sample_data = list(itertools.chain(*batch_data))
+    pipe = Pipeline(5, 3, 0)
+    with pipe:
+        ext_batch = fn.external_source(batch_data, cycle="quiet")
+        ext_sample = fn.external_source(sample_data, cycle="quiet", batch=False)
+        pipe.set_outputs(ext_batch, ext_sample)
+    pipe.build()
+    for epoch in range(2):
+        for i in range(len(batch_data)):
+            batch, sample = pipe.run()
+            N = len(batch_data[i])
+            assert len(batch) == N
+            assert len(sample) == N
+            check_output((batch,), batch_data[i])
+            check_output((sample,), batch_data[i])