diff --git a/codan/org.eclipse.cdt.codan.ui/src/org/eclipse/cdt/codan/internal/ui/preferences/ProblemsTreeEditor.java b/codan/org.eclipse.cdt.codan.ui/src/org/eclipse/cdt/codan/internal/ui/preferences/ProblemsTreeEditor.java
index 58749efb69e..fc044a9cf4b 100644
--- a/codan/org.eclipse.cdt.codan.ui/src/org/eclipse/cdt/codan/internal/ui/preferences/ProblemsTreeEditor.java
+++ b/codan/org.eclipse.cdt.codan.ui/src/org/eclipse/cdt/codan/internal/ui/preferences/ProblemsTreeEditor.java
@@ -293,7 +293,7 @@ public class ProblemsTreeEditor extends CheckedTreeEditor {
 
 			@Override
 			protected CellEditor getCellEditor(Object element) {
-				return new ComboBoxCellEditor(getTreeViewer().getTree(), CodanSeverity.stringValues());
+				return new ComboBoxCellEditor(getTreeViewer().getTree(), CodanSeverity.stringValues(), SWT.READ_ONLY);
 			}
 
 			@Override