diff --git a/doc/public/Headers.mk b/doc/public/Headers.mk
index 638bcad99..3194d233b 100644
--- a/doc/public/Headers.mk
+++ b/doc/public/Headers.mk
@@ -20,6 +20,7 @@ PRIVATE_TEST_HFILES = \
 	cairo-ps-test.h \
 	cairo-quartz-private.h \
 	cairo-wideint-private.h \
+	cairo-mutex-private.h \
 	cairo-path-fixed-private.h \
 	cairo-private.h \
 	cairo-ft-private.h \