diff --git a/src/include/firebird/fb_c_api.hdr b/src/include/firebird/fb_c_api.hdr
index 50a7c35234..27bb976b76 100644
--- a/src/include/firebird/fb_c_api.hdr
+++ b/src/include/firebird/fb_c_api.hdr
@@ -28,5 +28,7 @@
 
 #include <ibase.h>
 
+#ifndef FB_C_API_H
 struct IMaster* ISC_EXPORT fb_get_master_interface(void);
+#endif