diff --git a/src/mathed/InsetMathBig.cpp b/src/mathed/InsetMathBig.cpp
index cbd5c8a4f0..692d35d262 100644
--- a/src/mathed/InsetMathBig.cpp
+++ b/src/mathed/InsetMathBig.cpp
@@ -18,6 +18,7 @@
 
 #include "frontends/FontMetrics.h"
 
+#include "support/docstream.h"
 #include "support/lstrings.h"