diff --git a/devel/nasm/Makefile b/devel/nasm/Makefile
index 87a2f0d8facd..9b16a210141f 100644
--- a/devel/nasm/Makefile
+++ b/devel/nasm/Makefile
@@ -1,43 +1,43 @@
 PORTNAME=	nasm
-PORTVERSION=	2.16.01
+PORTVERSION=	2.15.05
 PORTEPOCH=	1
 CATEGORIES=	devel lang
 MASTER_SITES=	https://www.nasm.us/pub/nasm/releasebuilds/${PORTVERSION}/ \
 		https://mirror.sobukus.de/files/src/nasm/
 
 MAINTAINER=	salvadore@FreeBSD.org
 COMMENT=	General-purpose multi-platform x86 and amd64 assembler
 WWW=		https://www.nasm.us/
 
 LICENSE=	BSD2CLAUSE
 LICENSE_FILE=	${WRKSRC}/LICENSE
 
 USES=		compiler:c11 cpe gmake perl5 tar:xz
 CPE_VENDOR=	nasm
 CPE_PRODUCT=	netwide_assembler
 USE_PERL5=	build
 
 GNU_CONFIGURE=	yes
 CONFIGURE_ENV=	ac_cv_func_strspn=yes
 
 MAKE_ARGS+=	INSTALLROOT=${STAGEDIR}
 INSTALL_TARGET=	install #needed for RDOFF_INSTALL_TARGET
 
 PORTDOCS=	*
 
 OPTIONS_DEFINE=	DOCS RDOFF
 OPTIONS_SUB=	yes
 
 RDOFF_DESC=	Install tools to handle RDOFF object files
 
 DOCS_DISTFILES=	${DISTNAME}${EXTRACT_SUFX} \
 		${DISTNAME}-xdoc${EXTRACT_SUFX}
 
 RDOFF_INSTALL_TARGET=	install_rdf
 
 post-install-DOCS-on:
 	@${MKDIR} ${STAGEDIR}${DOCSDIR}
 	(cd ${WRKSRC}/doc && ${COPYTREE_SHARE} html ${STAGEDIR}${DOCSDIR})
 	${INSTALL_DATA} ${WRKSRC}/doc/nasmdoc.txt ${STAGEDIR}${DOCSDIR}
 
 .include <bsd.port.mk>
diff --git a/devel/nasm/distinfo b/devel/nasm/distinfo
index f94ae9bebad1..d67d2ab6f30d 100644
--- a/devel/nasm/distinfo
+++ b/devel/nasm/distinfo
@@ -1,5 +1,5 @@
-TIMESTAMP = 1671748109
-SHA256 (nasm-2.16.01.tar.xz) = c77745f4802375efeee2ec5c0ad6b7f037ea9c87c92b149a9637ff099f162558
-SIZE (nasm-2.16.01.tar.xz) = 1017732
-SHA256 (nasm-2.16.01-xdoc.tar.xz) = 801867a71f4c3d513a927ba09b3fa12ef9c7c5c98c0aaafc59c7f342faeab2c9
-SIZE (nasm-2.16.01-xdoc.tar.xz) = 867484
+TIMESTAMP = 1600344380
+SHA256 (nasm-2.15.05.tar.xz) = 3caf6729c1073bf96629b57cee31eeb54f4f8129b01902c73428836550b30a3f
+SIZE (nasm-2.15.05.tar.xz) = 995732
+SHA256 (nasm-2.15.05-xdoc.tar.xz) = 02a260cabb649bf55a06e3dc5abb1413746704156c80afc742b8fc1510262ed1
+SIZE (nasm-2.15.05-xdoc.tar.xz) = 823612
diff --git a/devel/nasm/files/patch-d85890aa.c b/devel/nasm/files/patch-d85890aa.c
new file mode 100644
index 000000000000..fb198aa1467c
--- /dev/null
+++ b/devel/nasm/files/patch-d85890aa.c
@@ -0,0 +1,301 @@
+--- Makefile.in.orig	2020-08-28 16:04:43 UTC
++++ Makefile.in
+@@ -75,7 +75,7 @@ endif
+ endif
+ 
+ .SUFFIXES:
+-.SUFFIXES: $(X) .$(O) .$(A) .xml .1 .c .i .s .txt
++.SUFFIXES: $(X) .$(O) .$(A) .xml .1 .c .i .s .txt .time
+ 
+ .PHONY: all doc rdf install clean distclean cleaner spotless install_rdf test
+ .PHONY: install_doc everything install_everything strip perlreq dist tags TAGS
+@@ -100,7 +100,10 @@ NDISASM = disasm/ndisasm.$(O)
+ NASM    = asm/nasm.$(O)
+ NDISASM = disasm/ndisasm.$(O)
+ 
+-LIBOBJ = stdlib/snprintf.$(O) stdlib/vsnprintf.$(O) stdlib/strlcpy.$(O) \
++PROGOBJ = $(NASM) $(NDISASM)
++PROGS   = nasm$(X) ndisasm$(X)
++
++LIBOBJ_NW = stdlib/snprintf.$(O) stdlib/vsnprintf.$(O) stdlib/strlcpy.$(O) \
+ 	stdlib/strnlen.$(O) stdlib/strrchrnul.$(O) \
+ 	\
+ 	nasmlib/ver.$(O) \
+@@ -122,7 +125,7 @@ LIBOBJ = stdlib/snprintf.$(O) stdlib/vsnprintf.$(O) st
+ 	x86/regs.$(O) x86/regvals.$(O) x86/regflags.$(O) x86/regdis.$(O) \
+ 	x86/disp8.$(O) x86/iflag.$(O) \
+ 	\
+-	asm/error.$(O) asm/warnings.$(O) \
++	asm/error.$(O) \
+ 	asm/floats.$(O) \
+ 	asm/directiv.$(O) asm/directbl.$(O) \
+ 	asm/pragma.$(O) \
+@@ -147,15 +150,20 @@ LIBOBJ = stdlib/snprintf.$(O) stdlib/vsnprintf.$(O) st
+ 	\
+ 	disasm/disasm.$(O) disasm/sync.$(O)
+ 
+-ALLOBJ = $(NASM) $(NDISASM) $(LIBOBJ)
++# Warnings depend on all source files, so handle them separately
++WARNOBJ   = asm/warnings.$(O)
+ 
++LIBOBJ    = $(LIBOBJ_NW) $(WARNOBJ)
++ALLOBJ_NW = $(PROGOBJ) $(LIBOBJ_NW)
++ALLOBJ    = $(PROGOBJ) $(LIBOBJ)
++
+ SUBDIRS  = stdlib nasmlib output asm disasm x86 common macros
+ XSUBDIRS = test doc nsis rdoff
+ DEPDIRS  = . include config x86 rdoff $(SUBDIRS)
+ #-- End File Lists --#
+ 
+ all: dirs
+-	$(MAKE) nasm$(X) ndisasm$(X) rdf
++	$(MAKE) $(PROGS) rdf
+ 
+ NASMLIB = libnasm.$(A)
+ 
+@@ -271,19 +279,31 @@ warnings:
+ 	$(RM_F) $(WARNFILES)
+ 	$(MAKE) asm/warnings.time
+ 
+-asm/warnings.time: $(ALLOBJ:.@OBJEXT@=.c)
++asm/warnings.time: $(ALLOBJ_NW:.$(O)=.c)
+ 	: > asm/warnings.time
+-	$(MAKE) $(WARNFILES)
++	$(MAKE) $(WARNFILES:=.time)
+ 
+-asm/warnings.c: asm/warnings.pl asm/warnings.time
++asm/warnings.c.time: asm/warnings.pl asm/warnings.time
+ 	$(RUNPERL) $(srcdir)/asm/warnings.pl c asm/warnings.c $(srcdir)
++	: > asm/warnings.c.time
+ 
+-include/warnings.h: asm/warnings.pl asm/warnings.time
++asm/warnings.c: asm/warnings.c.time
++	@: Side effect
++
++include/warnings.h.time: asm/warnings.pl asm/warnings.time
+ 	$(RUNPERL) $(srcdir)/asm/warnings.pl h include/warnings.h $(srcdir)
++	: > include/warnings.h.time
+ 
+-doc/warnings.src: asm/warnings.pl asm/warnings.time
++include/warnings.h: include/warnings.h.time
++	@: Side effect
++
++doc/warnings.src.time: asm/warnings.pl asm/warnings.time
+ 	$(RUNPERL) $(srcdir)/asm/warnings.pl doc doc/warnings.src $(srcdir)
++	: > doc/warnings.src.time
+ 
++doc/warnings.src : doc/warnings.src.time
++	@: Side effect
++
+ # Assembler token hash
+ asm/tokhash.c: x86/insns.dat x86/regs.dat asm/tokens.dat asm/tokhash.pl \
+ 	perllib/phash.ph
+@@ -385,10 +405,9 @@ manpages: nasm.1 ndisasm.1
+ # Generated manpages, also pregenerated for distribution
+ manpages: nasm.1 ndisasm.1
+ 
+-install: nasm$(X) ndisasm$(X)
++install: $(PROGS)
+ 	$(MKDIR_P) $(DESTDIR)$(bindir)
+-	$(INSTALL_PROGRAM) nasm$(X) $(DESTDIR)$(bindir)/nasm$(X)
+-	$(INSTALL_PROGRAM) ndisasm$(X) $(DESTDIR)$(bindir)/ndisasm$(X)
++	$(INSTALL_PROGRAM) $(PROGS) $(DESTDIR)$(bindir)/
+ 	$(MKDIR_P) $(DESTDIR)$(mandir)/man1
+ 	$(INSTALL_DATA) $(srcdir)/nasm.1 $(DESTDIR)$(mandir)/man1/nasm.1
+ 	$(INSTALL_DATA) $(srcdir)/ndisasm.1 $(DESTDIR)$(mandir)/man1/ndisasm.1
+@@ -397,7 +416,7 @@ clean:
+ 	for d in . $(SUBDIRS) $(XSUBDIRS); do \
+ 		$(RM_F) "$$d"/*.$(O) "$$d"/*.s "$$d"/*.i "$$d"/*.$(A) ; \
+ 	done
+-	$(RM_F) nasm$(X) ndisasm$(X)
++	$(RM_F) $(PROGS)
+ 	$(RM_F) nasm-*-installer-*.exe
+ 	$(RM_F) tags TAGS
+ 	$(RM_F) nsis/arch.nsh
+@@ -412,18 +431,18 @@ distclean: clean
+ 	done
+ 	$(RM_F) test/*.$(O)
+ 	$(RM_RF) autom4te*.cache
+-	$(RM_F) Makefile *.dep asm/warnings.time
++	$(RM_F) Makefile *.dep
+ 
+ cleaner: clean
+ 	$(RM_F) $(PERLREQ) *.1 nasm.spec
+ 	$(MAKE) -C doc clean
+-	$(RM_F) *.dep asm/warnings.time
++	$(RM_F) *.dep */*.time
+ 
+ spotless: distclean cleaner
+ 	$(RM_F) doc/Makefile
+ 
+ strip:
+-	$(STRIP) --strip-unneeded nasm$(X) ndisasm$(X)
++	$(STRIP) --strip-unneeded $(PROGS)
+ 
+ TAGS:
+ 	$(RM_F) TAGS
+@@ -496,13 +515,13 @@ splint:
+ splint:
+ 	splint -weak *.c
+ 
+-test: nasm$(X)
++test: $(PROGS)
+ 	cd test && $(RUNPERL) performtest.pl --nasm=../nasm *.asm
+ 
+-golden: nasm$(X)
++golden: $(PROGS)
+ 	cd test && $(RUNPERL) performtest.pl --golden --nasm=../nasm *.asm
+ 
+-travis: nasm$(X)
++travis: $(PROGS)
+ 	$(PYTHON3) travis/nasm-t.py run
+ 
+ #
+--- Mkfiles/msvc.mak.orig	2020-08-28 16:04:43 UTC
++++ Mkfiles/msvc.mak
+@@ -64,7 +64,10 @@ NDISASM = disasm\ndisasm.$(O)
+ NASM    = asm\nasm.$(O)
+ NDISASM = disasm\ndisasm.$(O)
+ 
+-LIBOBJ = stdlib\snprintf.$(O) stdlib\vsnprintf.$(O) stdlib\strlcpy.$(O) \
++PROGOBJ = $(NASM) $(NDISASM)
++PROGS   = nasm$(X) ndisasm$(X)
++
++LIBOBJ_NW = stdlib\snprintf.$(O) stdlib\vsnprintf.$(O) stdlib\strlcpy.$(O) \
+ 	stdlib\strnlen.$(O) stdlib\strrchrnul.$(O) \
+ 	\
+ 	nasmlib\ver.$(O) \
+@@ -86,7 +89,7 @@ LIBOBJ = stdlib\snprintf.$(O) stdlib\vsnprintf.$(O) st
+ 	x86\regs.$(O) x86\regvals.$(O) x86\regflags.$(O) x86\regdis.$(O) \
+ 	x86\disp8.$(O) x86\iflag.$(O) \
+ 	\
+-	asm\error.$(O) asm\warnings.$(O) \
++	asm\error.$(O) \
+ 	asm\floats.$(O) \
+ 	asm\directiv.$(O) asm\directbl.$(O) \
+ 	asm\pragma.$(O) \
+@@ -111,8 +114,13 @@ LIBOBJ = stdlib\snprintf.$(O) stdlib\vsnprintf.$(O) st
+ 	\
+ 	disasm\disasm.$(O) disasm\sync.$(O)
+ 
+-ALLOBJ = $(NASM) $(NDISASM) $(LIBOBJ)
++# Warnings depend on all source files, so handle them separately
++WARNOBJ   = asm\warnings.$(O)
+ 
++LIBOBJ    = $(LIBOBJ_NW) $(WARNOBJ)
++ALLOBJ_NW = $(PROGOBJ) $(LIBOBJ_NW)
++ALLOBJ    = $(PROGOBJ) $(LIBOBJ)
++
+ SUBDIRS  = stdlib nasmlib output asm disasm x86 common macros
+ XSUBDIRS = test doc nsis rdoff
+ DEPDIRS  = . include config x86 rdoff $(SUBDIRS)
+@@ -230,18 +238,30 @@ warnings:
+ 	$(RM_F) $(WARNFILES)
+ 	$(MAKE) asm\warnings.time
+ 
+-asm\warnings.time: $(ALLOBJ:.@OBJEXT@=.c)
++asm\warnings.time: $(ALLOBJ_NW:.$(O)=.c)
+ 	: > asm\warnings.time
+-	$(MAKE) $(WARNFILES)
++	$(MAKE) $(WARNFILES:=.time)
+ 
+-asm\warnings.c: asm\warnings.pl asm\warnings.time
++asm\warnings.c.time: asm\warnings.pl asm\warnings.time
+ 	$(RUNPERL) $(srcdir)\asm\warnings.pl c asm\warnings.c $(srcdir)
++	: > asm\warnings.c.time
+ 
+-include\warnings.h: asm\warnings.pl asm\warnings.time
++asm\warnings.c: asm\warnings.c.time
++	@: Side effect
++
++include\warnings.h.time: asm\warnings.pl asm\warnings.time
+ 	$(RUNPERL) $(srcdir)\asm\warnings.pl h include\warnings.h $(srcdir)
++	: > include\warnings.h.time
+ 
+-doc\warnings.src: asm\warnings.pl asm\warnings.time
++include\warnings.h: include\warnings.h.time
++	@: Side effect
++
++doc\warnings.src.time: asm\warnings.pl asm\warnings.time
+ 	$(RUNPERL) $(srcdir)\asm\warnings.pl doc doc\warnings.src $(srcdir)
++	: > doc\warnings.src.time
++
++doc\warnings.src : doc\warnings.src.time
++	@: Side effect
+ 
+ # Assembler token hash
+ asm\tokhash.c: x86\insns.dat x86\regs.dat asm\tokens.dat asm\tokhash.pl \
+--- Mkfiles/openwcom.mak.orig	2020-08-28 16:04:44 UTC
++++ Mkfiles/openwcom.mak
+@@ -53,7 +53,10 @@ NDISASM = disasm\ndisasm.$(O)
+ NASM    = asm\nasm.$(O)
+ NDISASM = disasm\ndisasm.$(O)
+ 
+-LIBOBJ = stdlib\snprintf.$(O) stdlib\vsnprintf.$(O) stdlib\strlcpy.$(O) &
++PROGOBJ = $(NASM) $(NDISASM)
++PROGS   = nasm$(X) ndisasm$(X)
++
++LIBOBJ_NW = stdlib\snprintf.$(O) stdlib\vsnprintf.$(O) stdlib\strlcpy.$(O) &
+ 	stdlib\strnlen.$(O) stdlib\strrchrnul.$(O) &
+ 	&
+ 	nasmlib\ver.$(O) &
+@@ -75,7 +78,7 @@ LIBOBJ = stdlib\snprintf.$(O) stdlib\vsnprintf.$(O) st
+ 	x86\regs.$(O) x86\regvals.$(O) x86\regflags.$(O) x86\regdis.$(O) &
+ 	x86\disp8.$(O) x86\iflag.$(O) &
+ 	&
+-	asm\error.$(O) asm\warnings.$(O) &
++	asm\error.$(O) &
+ 	asm\floats.$(O) &
+ 	asm\directiv.$(O) asm\directbl.$(O) &
+ 	asm\pragma.$(O) &
+@@ -100,8 +103,13 @@ LIBOBJ = stdlib\snprintf.$(O) stdlib\vsnprintf.$(O) st
+ 	&
+ 	disasm\disasm.$(O) disasm\sync.$(O)
+ 
+-ALLOBJ = $(NASM) $(NDISASM) $(LIBOBJ)
++# Warnings depend on all source files, so handle them separately
++WARNOBJ   = asm\warnings.$(O)
+ 
++LIBOBJ    = $(LIBOBJ_NW) $(WARNOBJ)
++ALLOBJ_NW = $(PROGOBJ) $(LIBOBJ_NW)
++ALLOBJ    = $(PROGOBJ) $(LIBOBJ)
++
+ SUBDIRS  = stdlib nasmlib output asm disasm x86 common macros
+ XSUBDIRS = test doc nsis rdoff
+ DEPDIRS  = . include config x86 rdoff $(SUBDIRS)
+@@ -243,18 +251,30 @@ warnings:
+ 	$(RM_F) $(WARNFILES)
+ 	$(MAKE) asm\warnings.time
+ 
+-asm\warnings.time: $(ALLOBJ:.@OBJEXT@=.c)
++asm\warnings.time: $(ALLOBJ_NW:.$(O)=.c)
+ 	: > asm\warnings.time
+-	$(MAKE) $(WARNFILES)
++	$(MAKE) $(WARNFILES:=.time)
+ 
+-asm\warnings.c: asm\warnings.pl asm\warnings.time
++asm\warnings.c.time: asm\warnings.pl asm\warnings.time
+ 	$(RUNPERL) $(srcdir)\asm\warnings.pl c asm\warnings.c $(srcdir)
++	: > asm\warnings.c.time
+ 
+-include\warnings.h: asm\warnings.pl asm\warnings.time
++asm\warnings.c: asm\warnings.c.time
++	@: Side effect
++
++include\warnings.h.time: asm\warnings.pl asm\warnings.time
+ 	$(RUNPERL) $(srcdir)\asm\warnings.pl h include\warnings.h $(srcdir)
++	: > include\warnings.h.time
+ 
+-doc\warnings.src: asm\warnings.pl asm\warnings.time
++include\warnings.h: include\warnings.h.time
++	@: Side effect
++
++doc\warnings.src.time: asm\warnings.pl asm\warnings.time
+ 	$(RUNPERL) $(srcdir)\asm\warnings.pl doc doc\warnings.src $(srcdir)
++	: > doc\warnings.src.time
++
++doc\warnings.src : doc\warnings.src.time
++	@: Side effect
+ 
+ # Assembler token hash
+ asm\tokhash.c: x86\insns.dat x86\regs.dat asm\tokens.dat asm\tokhash.pl &