diff --git a/ansible_collections/f5networks/f5_modules/plugins/module_utils/icontrol.py b/ansible_collections/f5networks/f5_modules/plugins/module_utils/icontrol.py
index eba4baf69..5b40a431a 100644
--- a/ansible_collections/f5networks/f5_modules/plugins/module_utils/icontrol.py
+++ b/ansible_collections/f5networks/f5_modules/plugins/module_utils/icontrol.py
@@ -483,19 +483,27 @@ def upload_file(client, url, src, dest=None):
     Raises:
         F5ModuleError: Raised if ``retries`` limit is exceeded.
     """
-    if isinstance(src, StringIO) or isinstance(src, BytesIO):
+    if isinstance(src, StringIO):
+        content_bytes = src.getvalue().encode('utf-8')
+        fileobj = BytesIO(content_bytes)
+        size = len(content_bytes)
+        is_file = False
+    elif isinstance(src, BytesIO):
         fileobj = src
+        fileobj.seek(0, os.SEEK_END)
+        size = fileobj.tell()
+        fileobj.seek(0)
+        is_file = False
     else:
         fileobj = open(src, 'rb')
-
-    try:
-        size = os.stat(src).st_size
-        is_file = True
-    except TypeError:
-        src.seek(0, os.SEEK_END)
-        size = src.tell()
-        src.seek(0)
-        is_file = False
+        try:
+            size = os.stat(src).st_size
+            is_file = True
+        except TypeError:
+            src.seek(0, os.SEEK_END)
+            size = src.tell()
+            src.seek(0)
+            is_file = False
 
     # This appears to be the largest chunk size that iControlREST can handle.
     #
diff --git a/ansible_collections/f5networks/f5_modules/tests/unit/module_utils/network/f5/test_icontrol_upload.py b/ansible_collections/f5networks/f5_modules/tests/unit/module_utils/network/f5/test_icontrol_upload.py
index 14a543373..7882293e7 100644
--- a/ansible_collections/f5networks/f5_modules/tests/unit/module_utils/network/f5/test_icontrol_upload.py
+++ b/ansible_collections/f5networks/f5_modules/tests/unit/module_utils/network/f5/test_icontrol_upload.py
@@ -253,6 +253,35 @@ def test_multi_chunk_forced_small_chunks_final_chunk_accurate(self):
                 )
             )
 
+    def test_stringio_multibyte_utf8_content_range_matches_actual_bytes(self):
+        """
+        Verify StringIO containing multibyte UTF-8 characters encodes to bytes
+        so Content-Range total and chunk ranges match actual transmitted bytes.
+        """
+        # Character count: 8 chars, but UTF-8 byte count: 10 bytes
+        # '\u00e9' is 2 bytes, '\u2014' is 3 bytes (3 ascii + 2 + 1 ascii + 3 + 1 ascii = 10 bytes)
+        content_str = u'abc\u00e9-\u2014x'
+        fileobj = StringIO(content_str)
+
+        self.client.api.post.return_value = Mock(status=200)
+        result = upload_file(self.client, self.url, fileobj, 'cert.crt')
+
+        assert result is True
+        assert self.client.api.post.call_count == 1
+
+        call_args = self.client.api.post.call_args
+        headers = call_args.kwargs.get('headers') or call_args[1]['headers']
+        data = call_args.kwargs.get('data') or call_args[1]['data']
+
+        content_range = headers['Content-Range']
+        range_part, total = content_range.split('/')
+        start, end = map(int, range_part.split('-'))
+
+        expected_bytes = content_str.encode('utf-8')
+        assert int(total) == len(expected_bytes)
+        assert (end - start + 1) == len(data)
+        assert data == expected_bytes
+
 
 if __name__ == '__main__':
     unittest.main()