diff --git a/litellm/llms/fireworks_ai/chat/transformation.py b/litellm/llms/fireworks_ai/chat/transformation.py
index 8407e8ab69..6b654ebdfd 100644
--- a/litellm/llms/fireworks_ai/chat/transformation.py
+++ b/litellm/llms/fireworks_ai/chat/transformation.py
@@ -185,11 +185,16 @@ class FireworksAIConfig(OpenAIGPTConfig):
         ):  # allow user to toggle this feature.
             return content
         if isinstance(content["image_url"], str):
-            content["image_url"] = f"{content['image_url']}#transform=inline"
+            # Skip base64 data URLs — appending #transform=inline corrupts the
+            # base64 payload and causes an "Incorrect padding" decode error on
+            # the Fireworks side.  Data URLs are already inlined by definition.
+            # Lower-case before checking: URI schemes are case-insensitive (RFC 3986).
+            if not content["image_url"].lower().startswith("data:"):
+                content["image_url"] = f"{content['image_url']}#transform=inline"
         elif isinstance(content["image_url"], dict):
-            content["image_url"][
-                "url"
-            ] = f"{content['image_url']['url']}#transform=inline"
+            url = content["image_url"]["url"]
+            if not url.lower().startswith("data:"):
+                content["image_url"]["url"] = f"{url}#transform=inline"
         return content
 
     def _transform_tools(
diff --git a/tests/llm_translation/test_fireworks_ai_translation.py b/tests/llm_translation/test_fireworks_ai_translation.py
index b9abbd501d..24c0d546e2 100644
--- a/tests/llm_translation/test_fireworks_ai_translation.py
+++ b/tests/llm_translation/test_fireworks_ai_translation.py
@@ -161,6 +161,24 @@ def test_document_inlining_example(disable_add_transform_inline_image_block):
             "vision-gpt",
             "http://example.com/image.png",
         ),
+        # data: URLs must never have #transform=inline appended — doing so
+        # corrupts the base64 payload (fixes #23583).
+        # URI schemes are case-insensitive (RFC 3986) so check all variants.
+        (
+            {"image_url": "data:image/png;base64,iVBORw0KGgo="},
+            "gpt-4",
+            "data:image/png;base64,iVBORw0KGgo=",
+        ),
+        (
+            {"image_url": {"url": "data:image/jpeg;base64,/9j/4AAQ=="}},
+            "gpt-4",
+            {"url": "data:image/jpeg;base64,/9j/4AAQ=="},
+        ),
+        (
+            {"image_url": "Data:image/png;base64,iVBORw0KGgo="},
+            "gpt-4",
+            "Data:image/png;base64,iVBORw0KGgo=",
+        ),
     ],
 )
 def test_transform_inline(content, model, expected_url):
diff --git a/tests/test_litellm/llms/fireworks_ai/chat/test_fireworks_ai_chat_transformation.py b/tests/test_litellm/llms/fireworks_ai/chat/test_fireworks_ai_chat_transformation.py
index 5d5aaa64c8..2b71b88356 100644
--- a/tests/test_litellm/llms/fireworks_ai/chat/test_fireworks_ai_chat_transformation.py
+++ b/tests/test_litellm/llms/fireworks_ai/chat/test_fireworks_ai_chat_transformation.py
@@ -110,6 +110,35 @@ def test_get_supported_openai_params_reasoning_effort():
     assert "reasoning_effort" not in unsupported_params
 
 
+def test_add_transform_inline_image_block_skips_data_urls():
+    """
+    data: URLs must not have #transform=inline appended — doing so corrupts the
+    base64 payload and raises binascii.Error: Incorrect padding on the Fireworks side.
+    Regression test for https://github.com/BerriAI/litellm/issues/23583
+    """
+    config = FireworksAIConfig()
+    data_url = "data:image/jpeg;base64,/9j/4AAQSkZJRgAB"
+
+    # str branch
+    str_content = {"type": "image_url", "image_url": data_url}
+    result = config._add_transform_inline_image_block(
+        str_content, model="non-vision-model", disable_add_transform_inline_image_block=False
+    )
+    assert result["image_url"] == data_url, "data URL must not be modified (str branch)"
+
+    # dict branch
+    dict_content = {"type": "image_url", "image_url": {"url": data_url}}
+    result = config._add_transform_inline_image_block(
+        dict_content, model="non-vision-model", disable_add_transform_inline_image_block=False
+    )
+    assert result["image_url"]["url"] == data_url, "data URL must not be modified (dict branch)"
+
+    # regular https URL should still get the suffix
+    https_content = {"type": "image_url", "image_url": "https://example.com/image.jpg"}
+    result = config._add_transform_inline_image_block(
+        https_content, model="non-vision-model", disable_add_transform_inline_image_block=False
+    )
+    assert result["image_url"].endswith("#transform=inline"), "https URL should get #transform=inline"
 @pytest.mark.parametrize(
     "api_base, expected_url_prefix",
     [