diff --git a/bblocks/import_tools/imf.py b/bblocks/import_tools/imf.py
index 216fbcb..eb56e67 100644
--- a/bblocks/import_tools/imf.py
+++ b/bblocks/import_tools/imf.py
@@ -26,7 +26,7 @@ def __post_init__(self) -> None:
         if (self.year is None and self.release is not None) or (
             self.year is not None and self.release is None
         ):
-            raise ValueError("Both year and release must be specified.")
+            raise ValueError("Both year and release must be specified or must both be `None`")
 
     def __repr__(self) -> str:
         return f"IMF WEO(year={self.year}, release={self.release})"
@@ -186,4 +186,4 @@ def get_data(
         if not keep_metadata:
             return df.filter(["iso_code", "name", "indicator", "year", "value"], axis=1)
 
-        return df
+        return df
\ No newline at end of file