diff --git a/x11-toolkits/fox16/Makefile b/x11-toolkits/fox16/Makefile
index 1bc5a9296234..9f521aad34cd 100644
--- a/x11-toolkits/fox16/Makefile
+++ b/x11-toolkits/fox16/Makefile
@@ -102,6 +102,7 @@ CONFIGURE_ARGS+=	--with-profiling=gprof
 .endif
 
 post-patch:
+	${REINPLACE_CMD} -e '/^Libs:/s|$$| ${PTHREAD_LIBS}|' ${WRKSRC}/fox.pc.in
 # CXXFLAGS safeness
 	@${REINPLACE_CMD} -E -e \
 		's|-O2|${CXXFLAGS}|g ; \
diff --git a/x11-toolkits/fox17/Makefile b/x11-toolkits/fox17/Makefile
index 619279bb44c2..20488aae50fd 100644
--- a/x11-toolkits/fox17/Makefile
+++ b/x11-toolkits/fox17/Makefile
@@ -48,6 +48,7 @@ BROKEN=		does not build on amd64
 .endif
 
 post-patch:
+	${REINPLACE_CMD} -e '/^Libs:/s|$$| ${PTHREAD_LIBS}|' ${WRKSRC}/fox17.pc.in
 .if defined(NOPORTDOCS)
 	${REINPLACE_CMD} -e '/^SUBDIRS/s/ doc//' ${WRKSRC}/Makefile.am ${WRKSRC}/Makefile.in
 .endif