diff --git a/tardis/io/config_reader.py b/tardis/io/config_reader.py
index 0eb61f90c59..c50af13a0ae 100644
--- a/tardis/io/config_reader.py
+++ b/tardis/io/config_reader.py
@@ -297,7 +297,7 @@ def from_config_dict(cls, config_dict, validate=True, config_dirname=""):
                 raise ValueError(
                     f"Initial Temperature of Inner Boundary Black Body is Invalid, {initial_t_inner}"
                 )
-            if initial_t_rad.value < 0:
+            if initial_t_rad.value < -1:
                 raise ValueError(
                     f"Initial Radiative Temperature is Invalid, {initial_t_rad}"
                 )