diff --git a/lib/clangimport.cpp b/lib/clangimport.cpp
index 98c0e700d83..e6fdbc3bb0d 100644
--- a/lib/clangimport.cpp
+++ b/lib/clangimport.cpp
@@ -1639,7 +1639,9 @@ void clangimport::parseClangAstDump(Tokenizer &tokenizer, std::istream &f)
         if (pos1 == std::string::npos)
             continue;
         if (!tree.empty() && line.substr(pos1) == "-<<<NULL>>>") {
-            const int level = (pos1 - 1) / 2;
+            const size_t level = (pos1 - 1) / 2;
+            if (level == 0 || level > tree.size())
+                continue;
             tree[level - 1]->children.push_back(nullptr);
             continue;
         }
diff --git a/test/testclangimport.cpp b/test/testclangimport.cpp
index 6a39b563982..26c73e5f7a2 100644
--- a/test/testclangimport.cpp
+++ b/test/testclangimport.cpp
@@ -139,6 +139,14 @@ class TestClangImport : public TestFixture {
         TEST_CASE(valueType2);
 
         TEST_CASE(crash);
+        TEST_CASE(nullNodeInvalidLevel);
+    }
+
+    void nullNodeInvalidLevel() {
+        // a "<<<NULL>>>" line whose indentation maps to level 0 must not index tree[-1]
+        const char* clang = "`-FunctionDecl 0x1 <a.cpp:1:1, col:34> col:6 foo 'void ()'\n"
+                            "`-<<<NULL>>>\n";
+        ASSERT_EQUALS("void foo ( ) ;", parse(clang));
     }
 
     std::string parse(const char clang[]) {