diff --git a/src/pl/plperl/ppport.h b/src/pl/plperl/ppport.h
index e89ab4fc0663a81aaf18e634595a6be7406a92a0..8c51dbbd538f4f52b5c0ace488e3f0962dab92b5 100644
--- a/src/pl/plperl/ppport.h
+++ b/src/pl/plperl/ppport.h
@@ -221,6 +221,7 @@ __DATA__
 /* Replace: 0 */
 #endif
 
+#ifndef PERL_UNUSED_DECL
 #ifdef HASATTRIBUTE
 #if (defined(__GNUC__) && defined(__cplusplus)) || defined(__INTEL_COMPILER)
 #define PERL_UNUSED_DECL
@@ -230,6 +231,7 @@ __DATA__
 #else
 #define PERL_UNUSED_DECL
 #endif
+#endif
 
 #ifndef dNOOP
 #define NOOP (void)0