diff --git a/ProcessLib/SourceTerms/SourceTermBuilder.cpp b/ProcessLib/SourceTerms/SourceTermBuilder.cpp
index cbf4cbf3527b75e47da1e2ca6e7abd9f2e203646..156bb4c9ecad7c74771126ae23099856f2233047 100644
--- a/ProcessLib/SourceTerms/SourceTermBuilder.cpp
+++ b/ProcessLib/SourceTerms/SourceTermBuilder.cpp
@@ -91,7 +91,7 @@ std::unique_ptr<NodalSourceTerm> SourceTermBuilder::createNodalSourceTerm(
     if (ids.size() != 1)
         OGS_FATAL(
             "Found %d nodes for nodal source term, but exactly one node is "
-            "required.");
+            "required.", ids.size());
 
     return ProcessLib::createNodalSourceTerm(
         config.config, dof_table, mesh.getID(), ids[0], variable_id,