diff --git a/debug/org.eclipse.cdt.debug.core/src/org/eclipse/cdt/debug/core/CDebugCorePlugin.java b/debug/org.eclipse.cdt.debug.core/src/org/eclipse/cdt/debug/core/CDebugCorePlugin.java
index d0fd7b73d68..b836bddb2f0 100644
--- a/debug/org.eclipse.cdt.debug.core/src/org/eclipse/cdt/debug/core/CDebugCorePlugin.java
+++ b/debug/org.eclipse.cdt.debug.core/src/org/eclipse/cdt/debug/core/CDebugCorePlugin.java
@@ -354,6 +354,11 @@ public class CDebugCorePlugin extends Plugin {
 			fCommonSourceLookupDirector = new CommonSourceLookupDirector();
 			String newMemento = CDebugCorePlugin.getDefault().getPluginPreferences().getString( ICDebugInternalConstants.PREF_COMMON_SOURCE_CONTAINERS );
 			if ( newMemento.length() == 0 ) {
+				// Add the participant(s). This happens as part of
+				// initializeFromMemento(), but since we're not calling it, we
+				// need to do this explicitly. See 299583.
+				fCommonSourceLookupDirector.initializeParticipants();
+				
 				// Convert source locations to source containers
 				convertSourceLocations( fCommonSourceLookupDirector );
 			}