diff --git a/eland/field_mappings.py b/eland/field_mappings.py
index 92ac7f7..d9998e0 100644
--- a/eland/field_mappings.py
+++ b/eland/field_mappings.py
@@ -42,6 +42,8 @@ from pandas.core.dtypes.common import (  # type: ignore
 )
 from pandas.core.dtypes.inference import is_list_like
 
+from .common import es_version
+
 if TYPE_CHECKING:
     from elasticsearch import Elasticsearch
     from numpy.typing import DTypeLike
@@ -213,7 +215,7 @@ class FieldMappings:
 
         # Get all fields (including all nested) and then all field_caps
         all_fields = FieldMappings._extract_fields_from_mapping(get_mapping)
-        all_fields_caps = client.field_caps(index=index_pattern, fields="*")
+        all_fields_caps = _compat_field_caps(client, index=index_pattern, fields="*")
 
         # Get top level (not sub-field multifield) mappings
         source_fields = FieldMappings._extract_fields_from_mapping(
@@ -925,3 +927,34 @@ def verify_mapping_compatibility(
             f"DataFrame dtypes and Elasticsearch index mapping "
             f"aren't compatible:\n{problems_message}"
         )
+
+
+def _compat_field_caps(client, fields, index=None):
+    """The field_caps API moved it's 'fields' parameter to the HTTP request body
+    in Elasticsearch 8.5.0 (previously was only accepted in the query string).
+    This can cause some unfortunate errors for users of Eland against old server
+    versions because at that point the version of the Elasticsearch client actually
+    matters for compatibility, which can be unexpected by consumers of *only* Eland.
+
+    Our work-around below is to force the parameter in the query string on older server versions.
+    """
+
+    # If the server version is 8.5.0 or later we don't need
+    # the query string work-around. Sending via any client
+    # version should be just fine.
+    if es_version(client) >= (8, 5, 0):
+        return client.field_caps(index=index, fields=fields)
+
+    # Otherwise we need to force sending via the query string.
+    from elasticsearch._sync.client import SKIP_IN_PATH, _quote
+
+    if index not in SKIP_IN_PATH:
+        __path = f"/{_quote(index)}/_field_caps"
+    else:
+        __path = "/_field_caps"
+    __query: Dict[str, Any] = {}
+    if fields is not None:
+        __query["fields"] = fields
+    return client.perform_request(
+        "POST", __path, params=__query, headers={"accept": "application/json"}
+    )
diff --git a/tests/field_mappings/test_compat_field_caps_pytest.py b/tests/field_mappings/test_compat_field_caps_pytest.py
new file mode 100644
index 0000000..867bf03
--- /dev/null
+++ b/tests/field_mappings/test_compat_field_caps_pytest.py
@@ -0,0 +1,60 @@
+#  Licensed to Elasticsearch B.V. under one or more contributor
+#  license agreements. See the NOTICE file distributed with
+#  this work for additional information regarding copyright
+#  ownership. Elasticsearch B.V. licenses this file to you under
+#  the Apache License, Version 2.0 (the "License"); you may
+#  not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+# 	http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing,
+#  software distributed under the License is distributed on an
+#  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+#  KIND, either express or implied.  See the License for the
+#  specific language governing permissions and limitations
+#  under the License.
+
+# File called _pytest for PyCharm compatability
+from unittest import mock
+
+from eland.field_mappings import _compat_field_caps
+from tests.common import TestData
+
+
+class TestCompatFieldCaps(TestData):
+    def test_query_for_es_8_4_4(self):
+        # Elasticsearch server <8.5.0 should use the raw perform_request()
+        client = mock.Mock()
+        client._eland_es_version = (8, 4, 4)
+
+        _compat_field_caps(client, fields="*", index="test-index")
+
+        client.perform_request.assert_called_with(
+            "POST",
+            "/test-index/_field_caps",
+            params={"fields": "*"},
+            headers={"accept": "application/json"},
+        )
+
+        _compat_field_caps(client, fields="*")
+
+        client.perform_request.assert_called_with(
+            "POST",
+            "/_field_caps",
+            params={"fields": "*"},
+            headers={"accept": "application/json"},
+        )
+
+    def test_query_for_es_8_5_0(self):
+        # Elasticsearch server >=8.5.0 should use the client API.
+        client = mock.Mock()
+        client._eland_es_version = (8, 5, 0)
+
+        _compat_field_caps(client, fields="*", index="test-index")
+
+        client.field_caps.assert_called_with(fields="*", index="test-index")
+
+        _compat_field_caps(client, fields="*")
+
+        client.field_caps.assert_called_with(fields="*", index=None)