diff --git a/src/systemd/_sd-common.h b/src/systemd/_sd-common.h
index 3bb886be75..97c3943861 100644
--- a/src/systemd/_sd-common.h
+++ b/src/systemd/_sd-common.h
@@ -22,8 +22,8 @@
 
 /* This is a private header; never even think of including this directly! */
 
-#if __INCLUDE_LEVEL__ <= 1
-#error "Do not include _sd-common.h directly; it is a private header."
+#if defined(__INCLUDE_LEVEL__) && __INCLUDE_LEVEL__ <= 1
+#  error "Do not include _sd-common.h directly; it is a private header."
 #endif
 
 #ifndef _sd_printf_