diff --git a/archivers/p7zip/Makefile b/archivers/p7zip/Makefile
index 69e8a1b271ad..316bcd10ab63 100644
--- a/archivers/p7zip/Makefile
+++ b/archivers/p7zip/Makefile
@@ -34,7 +34,7 @@ post-patch:
 		${WRKSRC}/man1/*
 	${MV} ${WRKSRC}/README ${WRKSRC}/DOCS/readme.unix
 
-.if ${SLAVE_PORT} == "no"
+.if defined(SLAVE_PORT) && ${SLAVE_PORT} == "no"
 do-install:
 	${MKDIR} ${STAGEDIR}${PREFIX}/libexec/p7zip
 .for BINARY in 7z 7za 7zr 7zCon.sfx