diff --git a/spectral.pro b/spectral.pro
index cee1437..1631b7b 100644
--- a/spectral.pro
+++ b/spectral.pro
@@ -43,6 +43,7 @@ $$USE_SYSTEM_CMARK {
     PKGCONFIG += libcmark
 } else {
     message("Falling back to built-in CMark.")
+    INCLUDEPATH += include/cmark
     HEADERS += \
         include/cmark/buffer.h \
         include/cmark/chunk.h \