diff --git a/src/gw/spectrum-spec.scm b/src/gw/spectrum-spec.scm
index 253464c..605796c 100644
--- a/src/gw/spectrum-spec.scm
+++ b/src/gw/spectrum-spec.scm
@@ -30,6 +30,7 @@
         "#include <painter_gdk.h>\n"
         "#include <burrow/nih.h>\n"
         "#include <hosbackingsim.h>\n"
+        "#include <guile-cairo/guile-cairo-smob-types.h>\n"
         "\n"))
 
         ; couple of disabled sources