diff --git a/include/alt-extra/psa/crypto.h b/include/alt-extra/psa/crypto.h
new file mode 100644
index 000000000..005f3aeea
--- /dev/null
+++ b/include/alt-extra/psa/crypto.h
@@ -0,0 +1,7 @@
+/* The goal of the include/alt-extra directory is to test what happens
+ * if certain files come _after_ the normal include directory.
+ * Make sure that if the alt-extra directory comes before the normal
+ * directory (so we wouldn't be achieving our test objective), the build
+ * will fail.
+ */
+#error "The normal include directory must come first in the include path"