diff --git a/notebooks/Gotthard2/Correction_Gotthard2_NBC.ipynb b/notebooks/Gotthard2/Correction_Gotthard2_NBC.ipynb
index a424d7f31a2d285fb92321b884d5b69d59be0d6f..c70f1b709914371bd81f5ba3298a798fc0317b67 100644
--- a/notebooks/Gotthard2/Correction_Gotthard2_NBC.ipynb
+++ b/notebooks/Gotthard2/Correction_Gotthard2_NBC.ipynb
@@ -241,9 +241,7 @@
     "    db_modules = [da_to_pdu[da] for da in karabo_da]\n",
     "\n",
     "print(f\"Process modules: {db_modules} for run {run}\")\n",
-    "if len(input_source_affixes) != len(karabo_da):\n",
-    "    raise ValueError(\n",
-    "        \"receiver_affixes & karabo_da are not the same length\")\n",
+    "\n",
     "\n",
     "da_to_source = gotthard2lib.map_da_to_source(\n",
     "    run_dc,\n",
diff --git a/src/cal_tools/gotthard2/gotthard2lib.py b/src/cal_tools/gotthard2/gotthard2lib.py
index 51f1e6118536ab4836c5ec7319c64b9d5a123c1b..f828f35418c80b0168d1cdc8cc10563f3e9a38e3 100644
--- a/src/cal_tools/gotthard2/gotthard2lib.py
+++ b/src/cal_tools/gotthard2/gotthard2lib.py
@@ -6,15 +6,19 @@ import extra_data
 
 
 def map_da_to_source(dc, das, source_template, karabo_id, affixes):
-    da_to_source = {}
-    for da, aff in zip(das, affixes):
-        sources = dc.select(
-            f"*{source_template.format(karabo_id=karabo_id, input_source_affixes=aff)}").all_sources  # noqa
-        if len(sources) != 1:
-            raise ValueError(f"No/multiple sources found for {aff!r}")
-        da_to_source[da] = list(sources)[0]
-
-    return da_to_source
+    source_names = [
+        f"{source_template.format(karabo_id=karabo_id, input_source_affixes=aff)}"  # noqa
+        for aff in affixes
+    ]
+    if len(source_names) != len(das):
+        raise ValueError(
+            "Number of source names (and given affixes) "
+            "does not match number of DAs")
+    missing_sources = set(source_names) - dc.instrument_sources
+    if missing_sources:
+        raise ValueError(
+            f"The following sources are missing from the run: {missing_sources}")
+    return dict(zip(das, source_names))
 
 
 class Gotthard2Ctrl():