diff --git a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/corext/codemanipulation/StubUtility.java b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/corext/codemanipulation/StubUtility.java
index c40bb7ab417..0e0cbcbf9cd 100644
--- a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/corext/codemanipulation/StubUtility.java
+++ b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/corext/codemanipulation/StubUtility.java
@@ -679,6 +679,8 @@ public class StubUtility {
 			ISourceRoot root = cproject.findSourceRoot(file);
 			if (root != null) {
 				path = PathUtil.makeRelativePath(path, root.getPath());
+			} else {
+				path = PathUtil.makeRelativePath(path, cproject.getPath());
 			}
 			return generateIncludeGuardSymbolFromFilePath(path.toString());