diff --git a/iso15118/secc/states/iso15118_2_states.py b/iso15118/secc/states/iso15118_2_states.py
index 87226b80..4a2d2c5c 100644
--- a/iso15118/secc/states/iso15118_2_states.py
+++ b/iso15118/secc/states/iso15118_2_states.py
@@ -647,9 +647,10 @@ async def process_message(
                     signature,
                 ) = self.generate_certificate_installation_res()
         except Exception as e:
-            logger.error(f"Error building CertificateInstallationRes: {e}")
+            error = f"Error building CertificateInstallationRes: {e}"
+            logger.error(error)
             self.stop_state_machine(
-                str(e),
+                error,
                 message,
                 ResponseCode.FAILED_NO_CERTIFICATE_AVAILABLE,
             )