diff --git a/mitogen/core.py b/mitogen/core.py
index 5be36a95d..c61658897 100644
--- a/mitogen/core.py
+++ b/mitogen/core.py
@@ -108,6 +108,11 @@ def _path_importer_cache(cls, path):
 except NameError:
     BaseException = Exception
 
+if sys.version_info >= (2, 6):
+    from io import BlockingIOError
+else:
+    BlockingIOError = None
+
 try:
     ModuleNotFoundError
 except NameError:
@@ -585,29 +590,63 @@ def io_op(func, *args):
     or :class:`OSError`, trapping UNIX error codes relating to disconnection
     and retry events in various subsystems:
 
-    * When a signal is delivered to the process on Python 2, system call retry
-      is signalled through :data:`errno.EINTR`. The invocation is automatically
-      restarted.
-    * When performing IO against a TTY, disconnection of the remote end is
-      signalled by :data:`errno.EIO`.
-    * When performing IO against a socket, disconnection of the remote end is
-      signalled by :data:`errno.ECONNRESET`.
-    * When performing IO against a pipe, disconnection of the remote end is
-      signalled by :data:`errno.EPIPE`.
-
+    :data:`errno.EINTR`
+        A system call was interrupted by a signal being delivered.
+        Python >= 3.5 retries most calls, forever (see PEP 475).
+        This wrapper retries all calls, also forever.
+
+    :exc:`BlockingIOError`
+    :data:`errno.EAGAIN`
+    :data:`errno.EWOULDBLOCK`
+        A system call on a non-blocking file would have blocked.
+        Python doesn't retry calls. It raises an exception or returns
+        :data:`None` - depending on the the call, the file, and the version.
+        This wrapper tries upto ``max_attempts`` times.
+
+    :data:`errno.EIO`
+    :data:`errno.ECONNRESET`
+    :data:`errno.EPIPE`
+        IO on a TTY, socket, or pipe respectively disconnected at the other end.
+
+    :param func:
+        The callable to run (e.g. :func:`os.read`, :func:`os.write`).
+    :param *args:
+        Positional arguments for the callable.
     :returns:
         Tuple of `(return_value, disconnect_reason)`, where `return_value` is
         the return value of `func(*args)`, and `disconnected` is an exception
         instance when disconnection was detected, otherwise :data:`None`.
     """
+    max_attempts = 5
+    attempt = 0
     while True:
+        attempt += 1
         try:
             return func(*args), None
+        except BlockingIOError:
+            e = sys.exc_info()[1]
+            _vv and IOLOG.debug(
+                'io_op(%r) attempt %d/%d -> %r', func, attempt, max_attempts, e
+            )
+            try:
+                written = e.characters_written
+            except AttributeError:
+                written = None
+            if written:
+                return written, None
+            if attempt < max_attempts:
+                continue
+            raise
         except (select.error, OSError, IOError):
             e = sys.exc_info()[1]
-            _vv and IOLOG.debug('io_op(%r) -> OSError: %s', func, e)
+            _vv and IOLOG.debug(
+                'io_op(%r) attempt %d/%d -> %r', func, attempt, max_attempts, e
+            )
             if e.args[0] == errno.EINTR:
                 continue
+            if e.args[0] in (errno.EAGAIN, errno.EWOULDBLOCK):
+                if attempt < max_attempts:
+                    continue
             if e.args[0] in (errno.EIO, errno.ECONNRESET, errno.EPIPE):
                 return None, e
             raise
diff --git a/tests/ansible/regression/files/generate_ascii_test_data.py b/tests/ansible/regression/files/generate_ascii_test_data.py
new file mode 100644
index 000000000..a1faad04b
--- /dev/null
+++ b/tests/ansible/regression/files/generate_ascii_test_data.py
@@ -0,0 +1,65 @@
+'''
+Write lines of deterministic ASCII test data
+
+```console
+$ python generate_ascii_test_data.py 192
+000000000000000000 mitogen-test-file ABCDEFGHIJKLMNOPQRSTUVWXYZ
+000000000000000064 mitogen-test-file BCDEFGHIJKLMNOPQRSTUVWXYZA
+000000000000000128 mitogen-test-file CDEFGHIJKLMNOPQRSTUVWXYZAB
+```
+'''
+
+import os
+import sys
+
+if sys.version_info < (3, 0):
+    range = xrange  # noqa: F821
+
+# Padding added to make each line LINE_SIZE bytes long, including a newline.
+# PADDING_POOL is repeated to eliminate repeated concatenations in the loop.
+PADDING_TEXT = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.encode('ascii')
+PADDING_SIZE = 26
+PADDING_POOL = PADDING_TEXT * 2
+
+LINE_TMPL = '%%018d mitogen-test-file %%.%ds\n'.encode('ascii') % PADDING_SIZE
+LINE_SIZE = 64
+
+def format_line(lineno):
+    # type: (int) -> bytes
+    line_offset = lineno * LINE_SIZE
+    padding_shift = lineno % PADDING_SIZE
+    return LINE_TMPL % (line_offset, PADDING_POOL[padding_shift:])
+
+
+def main():
+    assert len(PADDING_POOL) >= 2 * PADDING_SIZE
+    assert len(format_line(0)) == LINE_SIZE
+
+    try:
+        output_size = int(sys.argv[1])
+        if output_size < 0 or output_size % LINE_SIZE != 0:
+            raise ValueError
+    except IndexError:
+        prog = os.path.basename(sys.argv[0])
+        raise SystemExit('Usage: %s output_size [output_file]' % prog)
+    except ValueError:
+        raise SystemExit(
+            'Error: output_size must be >= 0 and a multiple of line size (%d), '
+            'got: %s' % (LINE_SIZE, sys.argv[1])
+        )
+
+    if len(sys.argv) >= 3 and sys.argv[2] != '-':
+        output_file = open(sys.argv[2], 'wb')
+    else:
+        output_file = os.fdopen(sys.stdout.fileno(), 'wb')
+
+    with output_file as f:
+        for lineno in range(0, output_size // LINE_SIZE):
+            line = format_line(lineno)
+            f.write(line)
+
+    raise SystemExit
+
+
+if __name__ == '__main__':
+    main()
diff --git a/tests/ansible/regression/issue_615__streaming_transfer.yml b/tests/ansible/regression/issue_615__streaming_transfer.yml
index 6fe52d55d..88a5e9f6a 100644
--- a/tests/ansible/regression/issue_615__streaming_transfer.yml
+++ b/tests/ansible/regression/issue_615__streaming_transfer.yml
@@ -7,30 +7,36 @@
   become: true
   vars:
     mitogen_ssh_compression: false
+    file_path_controller: "/tmp/fetch-{{ inventory_hostname }}-512mb.txt"
+    file_path_target: /tmp/mitogen-test-512mb.txt
+    file_size: "{{ 512 * 2**20 }}"
   tasks:
     - include_tasks: _mitogen_only.yml
     - block:
-        - name: Create /tmp/512mb.zero
-          shell: |
-            dd if=/dev/zero of=/tmp/512mb.zero bs=1048576 count=512;
-            chmod go= /tmp/512mb.zero
-          args:
-            creates: /tmp/512mb.zero
+        - name: Create test file on target
+          script:
+            cmd: generate_ascii_test_data.py "{{ file_size }}" "{{ file_path_target }}"
+            executable: "{{ ansible_python_interpreter | default(ansible_facts.discovered_interpreter_python) }}"
+            creates: "{{ file_path_target }}"
+          register: target_file_task
 
-        - name: Fetch /tmp/512mb.zero
+        - debug:
+            var: target_file_task
+
+        - name: Fetch test file
           fetch:
-            src: /tmp/512mb.zero
-            dest: /tmp/fetch-{{ inventory_hostname }}-512mb.zero
+            src: "{{ file_path_target }}"
+            dest: "{{ file_path_controller }}"
             flat: true
 
-        - name: Cleanup /tmp/512mb.zero
+        - name: Cleanup target
           file:
-            path: /tmp/512mb.zero
+            path: "{{ file_path_target }}"
             state: absent
 
-        - name: Cleanup fetched file
+        - name: Cleanup controller
           file:
-            path: /tmp/fetch-{{ inventory_hostname }}-512mb.zero
+            path: "{{ file_path_controller }}"
             state: absent
           become: false
           delegate_to: localhost