diff --git a/libs/langchain/langchain/chains/combine_documents/base.py b/libs/langchain/langchain/chains/combine_documents/base.py
index 2406cd4215f..298d9b64346 100644
--- a/libs/langchain/langchain/chains/combine_documents/base.py
+++ b/libs/langchain/langchain/chains/combine_documents/base.py
@@ -9,7 +9,9 @@ from langchain_core.callbacks import (
     CallbackManagerForChainRun,
 )
 from langchain_core.documents import Document
+from langchain_core.language_models import LanguageModelInput
 from langchain_core.prompts import BasePromptTemplate, PromptTemplate
+from langchain_core.runnables import Runnable, RunnableSequence
 from langchain_core.runnables.config import RunnableConfig
 from langchain_core.runnables.utils import create_model
 from langchain_text_splitters import RecursiveCharacterTextSplitter, TextSplitter
@@ -22,12 +24,23 @@ DOCUMENTS_KEY = "context"
 DEFAULT_DOCUMENT_PROMPT = PromptTemplate.from_template("{page_content}")
 
 
-def _validate_prompt(prompt: BasePromptTemplate, document_variable_name: str) -> None:
-    if document_variable_name not in prompt.input_variables:
-        raise ValueError(
-            f"Prompt must accept {document_variable_name} as an input variable. "
-            f"Received prompt with input variables: {prompt.input_variables}"
-        )
+def _validate_prompt(
+    prompt: Runnable[dict, LanguageModelInput], document_variable_name: str
+) -> None:
+    # validate that the prompt accepts the document variable if it starts with a prompt
+    # template
+    # if it's a generic runnable, don't validate
+    first_runnable = prompt
+    while isinstance(first_runnable, RunnableSequence):
+        first_runnable = first_runnable.first
+    if isinstance(first_runnable, BasePromptTemplate):
+        if document_variable_name not in first_runnable.input_variables:
+            msg = (
+                f"Prompt must accept {document_variable_name} as an input variable. "
+                "Received prompt with input variables: "
+                f"{first_runnable.input_variables}"
+            )
+            raise ValueError(msg)
 
 
 class BaseCombineDocumentsChain(Chain, ABC):