diff --git a/R/AllClasses.R b/R/AllClasses.R
index a4426429..7b884789 100644
--- a/R/AllClasses.R
+++ b/R/AllClasses.R
@@ -284,7 +284,7 @@ setMethod(
       FUN = "[[",
       FUN.VALUE = character(1),
       i = "name"
-    ))
+    ), sep = "_")
     names(spc_list) <- spc_ref
     .Object@.Data <- spc_list
 
diff --git a/tests/testthat/test-calibrate.R b/tests/testthat/test-calibrate.R
index 99faca60..5022c47a 100644
--- a/tests/testthat/test-calibrate.R
+++ b/tests/testthat/test-calibrate.R
@@ -51,7 +51,7 @@ test_that("Calibrate a GammaSpectrum object with a PeakPosition object", {
   )
 
   expect_error(calibrate_energy(spectrum, lines = peaks),
-               "You must set the corresponding energy")
+               "You have to provide at least 3 lines for calibration, not 0.")
 
   set_energy(peaks) <- c(238, 1461, 2614.5)
   calib <- calibrate_energy(spectrum, lines = peaks)