diff --git a/src/funcchain/schema/signature.py b/src/funcchain/schema/signature.py
index 1e81073..92701a4 100644
--- a/src/funcchain/schema/signature.py
+++ b/src/funcchain/schema/signature.py
@@ -14,7 +14,7 @@ class Signature(BaseModel):
     instruction: str
     """ Prompt instruction to the language model. """
 
-    input_args: list[tuple[str, type]] = Field(default_factory=list)
+    input_args: list[tuple[str, Any]] = Field(default_factory=list)
     """ List of input arguments for the prompt template. """
 
     output_types: list[Any]