diff --git a/third_party/agg23/agg_scanline_u.h b/third_party/agg23/agg_scanline_u.h
index 844dc9a..1db31c3 100644
--- a/third_party/agg23/agg_scanline_u.h
+++ b/third_party/agg23/agg_scanline_u.h
@@ -24,6 +24,8 @@
 #ifndef AGG_SCANLINE_U_INCLUDED
 #define AGG_SCANLINE_U_INCLUDED
 #include "agg_array.h"
+namespace pdfium
+{
 namespace agg
 {
 template<class CoverT> class scanline_u 
@@ -147,4 +149,5 @@
 };
 typedef scanline_u<int8u> scanline_u8;
 }
+}  // namespace pdfium
 #endif