diff --git a/ui/painter_agg2/agg_path_storage.h b/ui/painter_agg2/agg_path_storage.h
index 3c584d803..1ebe092c3 100644
--- a/ui/painter_agg2/agg_path_storage.h
+++ b/ui/painter_agg2/agg_path_storage.h
@@ -16,6 +16,8 @@
 #ifndef AGG_PATH_STORAGE_INCLUDED
 #define AGG_PATH_STORAGE_INCLUDED
 
+#include <assert.h>
+
 #include "agg_basics.h"
 
 namespace agg
@@ -316,6 +318,8 @@ namespace agg
         {
             allocate_block(nb);
         }
+
+        assert(m_coord_blocks);
         *xy_ptr = m_coord_blocks[nb] + ((m_total_vertices & block_mask) << 1);
         return m_cmd_blocks[nb] + (m_total_vertices & block_mask);
     }
diff --git a/ui/painter_agg2/agg_rendering_buffer.h b/ui/painter_agg2/agg_rendering_buffer.h
index fff79ded7..23ae6d779 100644
--- a/ui/painter_agg2/agg_rendering_buffer.h
+++ b/ui/painter_agg2/agg_rendering_buffer.h
@@ -20,6 +20,8 @@
 #ifndef AGG_RENDERING_BUFFER_INCLUDED
 #define AGG_RENDERING_BUFFER_INCLUDED
 
+#include <assert.h>
+
 #include "agg_basics.h"
 
 namespace agg
@@ -90,6 +92,7 @@ namespace agg
 
             T** rows = m_rows;
 
+            assert(height == 0 || m_rows);
             while(height--)
             {
                 *rows++ = row_ptr;