diff --git a/codan/org.eclipse.cdt.codan.core.cxx/src/org/eclipse/cdt/codan/core/cxx/model/AbstractCIndexChecker.java b/codan/org.eclipse.cdt.codan.core.cxx/src/org/eclipse/cdt/codan/core/cxx/model/AbstractCIndexChecker.java
index f2ca77c7c01..cb3d1df00b6 100644
--- a/codan/org.eclipse.cdt.codan.core.cxx/src/org/eclipse/cdt/codan/core/cxx/model/AbstractCIndexChecker.java
+++ b/codan/org.eclipse.cdt.codan.core.cxx/src/org/eclipse/cdt/codan/core/cxx/model/AbstractCIndexChecker.java
@@ -34,7 +34,7 @@ public abstract class AbstractCIndexChecker extends AbstractChecker implements I
 		return file;
 	}
 
-	void processFile(IFile file) throws CoreException, InterruptedException {
+	void  processFile(IFile file) throws CoreException, InterruptedException {
 		// create translation unit and access index
 		ICElement model = CoreModel.getDefault().create(file);
 		if (!(model instanceof ITranslationUnit)) return; // not a C/C++ file
@@ -52,7 +52,7 @@ public abstract class AbstractCIndexChecker extends AbstractChecker implements I
 		}
 	}
 
-	public boolean processResource(IResource resource) {
+	public synchronized boolean processResource(IResource resource) {
 		if (resource instanceof IFile) {
 			IFile file = (IFile) resource;
 			try {
diff --git a/codan/org.eclipse.cdt.codan.core.cxx/src/org/eclipse/cdt/codan/core/cxx/model/AbstractIndexAstChecker.java b/codan/org.eclipse.cdt.codan.core.cxx/src/org/eclipse/cdt/codan/core/cxx/model/AbstractIndexAstChecker.java
index c86b47b0bcd..7a1ce49f73b 100644
--- a/codan/org.eclipse.cdt.codan.core.cxx/src/org/eclipse/cdt/codan/core/cxx/model/AbstractIndexAstChecker.java
+++ b/codan/org.eclipse.cdt.codan.core.cxx/src/org/eclipse/cdt/codan/core/cxx/model/AbstractIndexAstChecker.java
@@ -61,6 +61,7 @@ public abstract class AbstractIndexAstChecker extends AbstractChecker implements
 			// create index based ast
 			IASTTranslationUnit ast = tu.getAST(index,
 					ITranslationUnit.AST_SKIP_INDEXED_HEADERS);
+			if (ast==null) return;//
 			// traverse the ast using the visitor pattern.
 			this.file = file;
 			processAst(ast);
@@ -70,7 +71,7 @@ public abstract class AbstractIndexAstChecker extends AbstractChecker implements
 		}
 	}
 
-	public boolean processResource(IResource resource) {
+	public synchronized boolean processResource(IResource resource) {
 		if (resource instanceof IFile) {
 			IFile file = (IFile) resource;
 			try {