diff --git a/src/libs/cplusplus/pp-engine.cpp b/src/libs/cplusplus/pp-engine.cpp
index c362c6fcf53dd6e46f3b85ab03af4589397870e7..bb6b6bebf8fcb27ee1a160765756efb30157b251 100644
--- a/src/libs/cplusplus/pp-engine.cpp
+++ b/src/libs/cplusplus/pp-engine.cpp
@@ -581,7 +581,8 @@ QByteArray Preprocessor::expand(const QByteArray &source)
 
 void Preprocessor::expand(const QByteArray &source, QByteArray *result)
 {
-    _expand(source, result);
+    if (result)
+        _expand(source, result);
 }
 
 void Preprocessor::expand(const char *first, const char *last, QByteArray *result)