Index: Mk/bsd.default-versions.mk
===================================================================
--- Mk/bsd.default-versions.mk	(revision 555694)
+++ Mk/bsd.default-versions.mk	(working copy)
@@ -51,7 +51,7 @@
 .if ${ARCH} == "powerpcspe"
 GCC_DEFAULT?=		8
 .else
-GCC_DEFAULT?=		9
+GCC_DEFAULT?=		10
 .endif
 # Possible values: 7, 8, 9, agpl
 GHOSTSCRIPT_DEFAULT?=	agpl
Index: biology/molden/Makefile
===================================================================
--- biology/molden/Makefile	(revision 555694)
+++ biology/molden/Makefile	(working copy)
@@ -39,6 +39,13 @@
 OPTIONS_DEFINE=		DATA DOCS
 OPTIONS_DEFAULT=	DATA
 
+.include <bsd.port.pre.mk>
+
+.if ${GCC_DEFAULT} >= 10
+# workaround for Type mismatch between actual argument at (1) and actual argument at (2) (REAL(8)/REAL(4)).
+FFLAGS+=	-fallow-argument-mismatch
+.endif
+
 post-patch:
 	@${REINPLACE_CMD} -e \
 		's|^CC |#CC | ; \
Index: cad/calculix-ccx/Makefile
===================================================================
--- cad/calculix-ccx/Makefile	(revision 555694)
+++ cad/calculix-ccx/Makefile	(working copy)
@@ -55,6 +55,11 @@
 FFLAGS+=	-fpic
 .endif
 
+.if ${GCC_DEFAULT} >= 10
+# workaround for Missing actual argument for argument '_formal_15' at (1)
+FFLAGS+=	-fallow-argument-mismatch
+.endif
+
 pre-build:
 	@${REINPLACE_CMD} -e 's+%%FC%%+${FC}+g ; s+%%CC%%+${CC}+g ; \
 	s+%%BLAS_LIBS%%+${BLASLIB}+ ; \
Index: comms/wsjtx/Makefile
===================================================================
--- comms/wsjtx/Makefile	(revision 555694)
+++ comms/wsjtx/Makefile	(working copy)
@@ -36,6 +36,13 @@
 
 _PATCHES=	wsjtx.patch hamlib.patch
 
+.include <bsd.port.pre.mk>
+
+.if ${GCC_DEFAULT} >= 10
+# workaround for More actual than formal arguments in procedure call at (1)
+FFLAGS+=	-fallow-argument-mismatch
+.endif
+
 post-patch:
 .  for _patch in ${_PATCHES}
 	# Keep a copy of the blank patch for the post-build target below
Index: databases/mariadb105-server/Makefile
===================================================================
--- databases/mariadb105-server/Makefile	(revision 555694)
+++ databases/mariadb105-server/Makefile	(working copy)
@@ -212,7 +212,7 @@
 .endif
 
 .if ${ARCH} == i386
-USE_GCC=	yes
+USE_GCC=	9
 CFLAGS+=	-DHAVE_GCC_C11_ATOMICS -latomic -DUSE_NEW_READLINE_INTERFACE
 CXXFLAGS+=	-fpermissive
 .endif
Index: games/libretro-paralleln64/Makefile
===================================================================
--- games/libretro-paralleln64/Makefile	(revision 555694)
+++ games/libretro-paralleln64/Makefile	(working copy)
@@ -30,8 +30,14 @@
 
 PLIST_FILES=	lib/libretro/parallel_n64_libretro.so
 
+.include <bsd.port.pre.mk>
+
+.if ${GCC_DEFAULT} >= 10
+BROKEN=		fails to link: ./mupen64plus-core/src/dd/dd_disk.o:(.bss+0xc): multiple definition of `CUR_BLOCK'
+.endif
+
 do-install:
 	${MKDIR} ${STAGEDIR}/${PREFIX}/lib/libretro;
 	${INSTALL_LIB} ${WRKSRC}/parallel_n64_libretro.so ${STAGEDIR}/${PREFIX}/lib/libretro;
 
-.include <bsd.port.mk>
+.include <bsd.port.post.mk>
Index: math/hs-penrose/Makefile
===================================================================
--- math/hs-penrose/Makefile	(revision 555694)
+++ math/hs-penrose/Makefile	(working copy)
@@ -135,4 +135,10 @@
 		x509-1.7.5_1 \
 		zlib-0.6.2.1_1
 
+.include <bsd.port.pre.mk>
+
+.if ${GCC_DEFAULT} >= 10
+BROKEN=		fails to build with GCC 10: cabal: Missing dependency on a foreign library: Missing (or bad) C library: gfortran
+.endif
+
 .include <bsd.port.mk>
Index: math/mumps/Makefile
===================================================================
--- math/mumps/Makefile	(revision 556537)
+++ math/mumps/Makefile	(working copy)
@@ -43,6 +43,11 @@
 .include <bsd.port.pre.mk>
 .include "${.CURDIR}/../../french/aster/bsd.aster.mk"
 
+.if ${GCC_DEFAULT} >= 10
+# workaround for Type mismatch in argument 's' at (1); passed INTEGER(4) to LOGICAL(4)
+FCFLAGS+=	-fallow-argument-mismatch
+.endif
+
 .ifdef WITH_MPI
 PKGNAMESUFFIX+=		-mpich
 .endif
Index: math/octave-forge-optiminterp/Makefile
===================================================================
--- math/octave-forge-optiminterp/Makefile	(revision 555694)
+++ math/octave-forge-optiminterp/Makefile	(working copy)
@@ -24,8 +24,16 @@
 
 MAKE_ENV+=	MKOCTFILE_FORTRAN_90=yes MKOCTFILE=mkoctfile
 
+.include <bsd.port.pre.mk>
+
+.if ${GCC_DEFAULT} >= 10
+# workaround for Rank mismatch between actual argument at (1) and actual argument at (2) (scalar and rank-2)
+# in theory, this should set FCFLAGS, but the port does not conform
+FFLAGS+=	-fallow-argument-mismatch
+.endif
+
 post-build:
 	${RM} ${WRKSRC}/Makefile ${WRKSRC}/configure
 	cd ${WRKDIR} && ${TAR} cfz ${DISTNAME}.tar.gz ${OCTSRC}
 
-.include <bsd.port.mk>
+.include <bsd.port.post.mk>
Index: math/scilab/Makefile
===================================================================
--- math/scilab/Makefile	(revision 555694)
+++ math/scilab/Makefile	(working copy)
@@ -129,6 +129,13 @@
 CONFIGURE_ARGS+=	--enable-debug
 .endif
 
+.include <bsd.port.pre.mk>
+
+.if ${GCC_DEFAULT} >= 10
+# workaround for Rank mismatch between actual argument at (1) and actual argument at (2) (rank-1 and scalar)
+FFLAGS+=	-fallow-argument-mismatch
+.endif
+
 post-patch:
 	@${REINPLACE_CMD} 's,/usr/local,${LOCALBASE},' ${WRKSRC}/etc/librarypath.xml
 	@${REINPLACE_CMD} -e 's, gfortran, ${FC},' ${WRKSRC}/modules/dynamic_link/src/scripts/configure
Index: net/iaxmodem/Makefile
===================================================================
--- net/iaxmodem/Makefile	(revision 555694)
+++ net/iaxmodem/Makefile	(working copy)
@@ -31,7 +31,7 @@
 
 .if ${ARCH} == i386 && ${CHOSEN_COMPILER_TYPE} == clang
 # gsm0610_rpe.c:81:10: error: invalid operand for instruction
-USE_GCC=	yes
+USE_GCC=	9
 .endif
 
 post-patch:
Index: science/cp2k/Makefile
===================================================================
--- science/cp2k/Makefile	(revision 555694)
+++ science/cp2k/Makefile	(working copy)
@@ -66,6 +66,10 @@
 	fi
 .endif
 
+.if ${GCC_DEFAULT} >= 10
+BROKEN=		fails to build with GCC 10: Element of assumed-shape or pointer array as actual argument at (1) cannot correspond to actual argument at (2)
+.endif
+
 post-patch:
 	@${REINPLACE_CMD} -i '' 's|LIBS.*=.*|& ${LDFLAGS}|; s|^FCFLAGS.*=.*|& -I${LOCALBASE}/include|; s| -march=native||' ${WRKSRC}/arch/FreeBSD-*
 
Index: science/elmerfem/Makefile
===================================================================
--- science/elmerfem/Makefile	(revision 555694)
+++ science/elmerfem/Makefile	(working copy)
@@ -74,6 +74,12 @@
 FFLAGS+=	-fPIC
 .endif
 
+.if ${GCC_DEFAULT} >= 10
+# workaround for Type mismatch between actual argument at (1) and actual argument at (2) (REAL(8)/COMPLEX(8)).
+# in theory, this should set FCFLAGS, but the port does not conform
+FFLAGS+=	-fallow-argument-mismatch
+.endif
+
 post-patch:
 	@${RM} -r ${WRKSRC}/elmergrid/src/metis-5.1.0
 	@${REINPLACE_CMD} -e 's,"metis.*/metis\.h",<metis.h>,' \
Index: science/getdp/Makefile
===================================================================
--- science/getdp/Makefile	(revision 555694)
+++ science/getdp/Makefile	(working copy)
@@ -20,6 +20,13 @@
 
 OPTIONS_DEFINE=	DOCS EXAMPLES
 
+.include <bsd.port.pre.mk>
+
+.if ${GCC_DEFAULT} >= 10
+# workaround for Rank mismatch in argument 'lines' at (1) (rank-1 and scalar)
+FFLAGS+=	-fallow-argument-mismatch
+.endif
+
 do-test:
 	cd ${WRKSRC}/demos && yes "" | ${STAGEDIR}${PREFIX}/bin/${PORTNAME} magnet.pro -solve MagSta_phi
 
Index: science/libgridxc/Makefile
===================================================================
--- science/libgridxc/Makefile	(revision 555694)
+++ science/libgridxc/Makefile	(working copy)
@@ -37,6 +37,12 @@
 LIBXC_LIB_DEPENDS=	libxc.so:science/libxc
 LIBXC_BROKEN=		Fails to build with libxc-5.0.0: https://bugs.launchpad.net/libgridxc/+bug/1899578
 
+.include <bsd.port.pre.mk>
+
+.if ${GCC_DEFAULT} >= 10
+BROKEN=		fails to build with GCC 10: Type mismatch between actual argument at (1) and actual argument at (2) (INTEGER(8)/INTEGER(4)).
+.endif
+
 post-patch:
 	@${MKDIR} ${BUILD_WRKSRC}
 	@${CAT} ${WRKSRC}/../extra/fortran.mk \
Index: science/pnetcdf/Makefile
===================================================================
--- science/pnetcdf/Makefile	(revision 555694)
+++ science/pnetcdf/Makefile	(working copy)
@@ -37,6 +37,13 @@
 OPENMPI3_CONFIGURE_ON=	--with-mpi=${LOCALBASE}/mpi/openmpi3
 OPENMPI3_LIB_DEPENDS=	libmpi.so:net/openmpi3
 
+.include <bsd.port.pre.mk>
+
+.if ${GCC_DEFAULT} >= 10
+# workaround for Type mismatch between actual argument at (1) and actual argument at (2) (INTEGER(8)/CHARACTER(*)).
+FCFLAGS+=	-fallow-argument-mismatch
+.endif
+
 post-patch:
 	@${REINPLACE_CMD} -e '/$$(INSTALL.*$$(PREFIX)/ s|$$(PREFIX)|$$(DESTDIR)&|' ${WRKSRC}/Makefile.in