diff --git a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/workingsets/IWorkingSetProjectConfigurationFactory.java b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/workingsets/IWorkingSetProjectConfigurationFactory.java
index 5edef550059..0fe3241f0b0 100644
--- a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/workingsets/IWorkingSetProjectConfigurationFactory.java
+++ b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/workingsets/IWorkingSetProjectConfigurationFactory.java
@@ -170,16 +170,23 @@ public interface IWorkingSetProjectConfigurationFactory {
 				result = new String[0];
 			}
 
+			for (String natureId : result) {
+				if (projectNaturePartOrdering.get(natureId) == null) {
+					// re-do nature cache. Some natures were added recently
+					projectNaturePartOrdering = computeProjectNaturePartOrdering();
+					break;
+				}
+			}
+
 			if (result.length > 0) {
 				Arrays.sort(result, new Comparator<String>() {
 					@Override
 					public int compare(String nature1, String nature2) {
 						Set<String> required1 = projectNaturePartOrdering.get(nature1);
 						Set<String> required2 = projectNaturePartOrdering.get(nature2);
-
-						if (required1.contains(nature2)) {
+						if (required1 != null && required1.contains(nature2)) {
 							return -1; // required1 precedes required2
-						} else if (required2.contains(nature1)) {
+						} else if (required2 != null && required2.contains(nature1)) {
 							return +1; // required2 precedes required1
 						} else if (nature1.startsWith("org.eclipse.cdt.") //$NON-NLS-1$
 								&& !nature2.startsWith("org.eclipse.cdt.")) { //$NON-NLS-1$