diff --git a/src/csgtermnormalizer.cc b/src/csgtermnormalizer.cc
index 461e965f..2f79841c 100644
--- a/src/csgtermnormalizer.cc
+++ b/src/csgtermnormalizer.cc
@@ -32,6 +32,22 @@ shared_ptr<CSGTerm> CSGTermNormalizer::normalize(const shared_ptr<CSGTerm> &root
 	return temp;
 }
 
+/*!
+	After aborting, a subtree might have become invalidated (NULL child term)
+	since terms can be instantiated multiple times.
+	This will search for NULL children an recursively repair the corresponding
+	subtree.
+ */
+shared_ptr<CSGTerm> CSGTermNormalizer::cleanup_term(shared_ptr<CSGTerm> &t)
+{
+	if (t->type != CSGTerm::TYPE_PRIMITIVE) {
+		if (t->left) t->left = cleanup_term(t->left);
+		if (t->right) t->right = cleanup_term(t->right);
+		return collapse_null_terms(t);
+	}
+	else return t;
+}
+
 shared_ptr<CSGTerm> CSGTermNormalizer::normalizePass(shared_ptr<CSGTerm> term)
 {
 	// This function implements the CSG normalization
@@ -62,7 +78,13 @@ shared_ptr<CSGTerm> CSGTermNormalizer::normalizePass(shared_ptr<CSGTerm> term)
 	if (!this->aborted) term->right = normalizePass(term->right);
 
 	// FIXME: Do we need to take into account any transformation of item here?
-	return collapse_null_terms(term);
+	shared_ptr<CSGTerm> t = collapse_null_terms(term);
+
+	if (this->aborted) {
+		if (t) t = cleanup_term(t);
+	}
+
+	return t;
 }
 
 shared_ptr<CSGTerm> CSGTermNormalizer::collapse_null_terms(const shared_ptr<CSGTerm> &term)
diff --git a/src/csgtermnormalizer.h b/src/csgtermnormalizer.h
index f7a444f6..bb55141e 100644
--- a/src/csgtermnormalizer.h
+++ b/src/csgtermnormalizer.h
@@ -15,6 +15,7 @@ private:
 	shared_ptr<CSGTerm> normalizePass(shared_ptr<CSGTerm> term) ;
 	bool match_and_replace(shared_ptr<CSGTerm> &term);
 	shared_ptr<CSGTerm> collapse_null_terms(const shared_ptr<CSGTerm> &term);
+	shared_ptr<CSGTerm> cleanup_term(shared_ptr<CSGTerm> &t);
 	unsigned int count(const shared_ptr<CSGTerm> &term) const;
 
 	bool aborted;