diff --git a/src/runtime/c/pgf/linearizer.h b/src/runtime/c/pgf/linearizer.h
index 9d2d607ee..816181090 100644
--- a/src/runtime/c/pgf/linearizer.h
+++ b/src/runtime/c/pgf/linearizer.h
@@ -2,7 +2,6 @@
 #define PGF_LINEARIZER_H_
 
 #include <gu/enum.h>
-#include <pgf/data.h>
 
 /// Linearization of abstract syntax trees.
 
@@ -13,6 +12,8 @@
 /// A concrete syntax tree
 typedef GuVariant PgfCncTree;
 
+#ifdef PGF_DATA_H_
+
 typedef enum {
 	PGF_CNC_TREE_APP,
 	PGF_CNC_TREE_CHUNKS,
@@ -47,6 +48,8 @@ typedef struct {
 	PgfLiteral lit;
 } PgfCncTreeLit;
 
+#endif
+
 /// An enumeration of #PgfCncTree trees.
 typedef GuEnum PgfCncTreeEnum;