diff --git a/libs/partners/openai/langchain_openai/chat_models/base.py b/libs/partners/openai/langchain_openai/chat_models/base.py
index 4b43236b68f..5cbd466f15e 100644
--- a/libs/partners/openai/langchain_openai/chat_models/base.py
+++ b/libs/partners/openai/langchain_openai/chat_models/base.py
@@ -3529,7 +3529,7 @@ def _resize(width: int, height: int) -> tuple[int, int]:
             width = (width * 768) // height
             height = 768
         else:
-            height = (width * 768) // height
+            height = (height * 768) // width
             width = 768
     return width, height
 
diff --git a/libs/partners/openai/tests/unit_tests/chat_models/test_base.py b/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
index 1cfb0943566..a7e84f672f1 100644
--- a/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
+++ b/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
@@ -76,6 +76,7 @@ from langchain_openai.chat_models.base import (
     _make_computer_call_output_from_message,
     _model_prefers_responses_api,
     _oai_structured_outputs_parser,
+    _resize,
 )
 
 
@@ -1068,6 +1069,12 @@ def test__create_usage_metadata_responses() -> None:
     )
 
 
+def test__resize_caps_dimensions_preserving_ratio() -> None:
+    """Larger side capped at 2048 then smaller at 768 keeping aspect ratio."""
+    assert _resize(2048, 4096) == (768, 1536)
+    assert _resize(4096, 2048) == (1536, 768)
+
+
 def test__convert_to_openai_response_format() -> None:
     # Test response formats that aren't tool-like.
     response_format: dict = {