diff --git a/expconfig.py b/expconfig.py
index c31a27b4b24b144787cdadc08e532c02c70f8ea2..87ffed38cf7a6baf78b34a04dfef0ca19aa932f6 100644
--- a/expconfig.py
+++ b/expconfig.py
@@ -400,7 +400,7 @@ class ExpConfig(ConfigObj):
                 elif not isinstance(value, dict):
                     value = value.replace('$', '$$')
             except (InterpolationError, ValueError) as error:
-                raise ExpConfigError(error.message, key)
+                raise ExpConfigError(str(error), key)
             section[key] = value
 
         # Undo remaining changes from walk with eval_key
@@ -412,7 +412,7 @@ class ExpConfig(ConfigObj):
                 elif not isinstance(value, dict):
                     value = value.replace('$$', '$')
             except (InterpolationError, ValueError) as error:
-                raise ExpConfigError(error.message, key)
+                raise ExpConfigError(str(error), key)
             section[key] = value
 
         # Move version info from local config to global list