diff --git a/qpdf/build.mk b/qpdf/build.mk
index 36224090..e5f926f1 100644
--- a/qpdf/build.mk
+++ b/qpdf/build.mk
@@ -26,6 +26,8 @@ TC_SRCS_qpdf = $(wildcard libqpdf/*.cc) $(wildcard qpdf/*.cc)
 
 # -----
 
+XCFLAGS_qpdf_qpdf-ctest := -Ilibqpdf
+
 define use_wmain
   XCXXFLAGS_qpdf_$(1) := $(WINDOWS_WMAIN_COMPILE)
   XLDFLAGS_qpdf_$(1) := $(WINDOWS_WMAIN_LINK)
diff --git a/qpdf/qpdf-ctest.c b/qpdf/qpdf-ctest.c
index 36a50f11..dff7c8c4 100644
--- a/qpdf/qpdf-ctest.c
+++ b/qpdf/qpdf-ctest.c
@@ -4,7 +4,8 @@
 #include <stdlib.h>
 #include <string.h>
 #include <errno.h>
-#include "../libqpdf/qpdf/qpdf-config.h" // for LL_FMT
+
+#include <qpdf/qpdf-config.h> // for LL_FMT -- special case in build
 
 static char* whoami = 0;
 static qpdf_data qpdf = 0;