diff --git a/.gitignore b/.gitignore
index c02b2831c06537ed34798adc03f035bb35542062..fae449fb0390f55a6bd2db28cd44e446f2894b19 100644
--- a/.gitignore
+++ b/.gitignore
@@ -13,7 +13,7 @@
 *.bak
 .coqdeps.d
 .coq-native/
-build-dep/
+builddep/
 Makefile.coq
 Makefile.coq.conf
 .Makefile.coq.d
diff --git a/Makefile b/Makefile
index 8d615e4b2c9081e20b16fb3931cea5ef951c540c..ac8dba01d935c2dbd09966a33cc7afa229b68cfa 100644
--- a/Makefile
+++ b/Makefile
@@ -1,42 +1,55 @@
-# Forward most targets to Coq makefile (with some trick to make this phony)
-%: Makefile.coq phony
-	+@make -f Makefile.coq $@
-
+# Default target
 all: Makefile.coq
-	+@make -f Makefile.coq all
+	+@$(MAKE) -f Makefile.coq all
 .PHONY: all
 
+# Permit local customization
+-include Makefile.local
+
+# Forward most targets to Coq makefile (with some trick to make this phony)
+%: Makefile.coq phony
+	@#echo "Forwarding $@"
+	+@$(MAKE) -f Makefile.coq $@
+phony: ;
+.PHONY: phony
+
 clean: Makefile.coq
-	+@make -f Makefile.coq clean
-	find theories tests \( -name "*.d" -o -name "*.vo" -o -name "*.aux" -o -name "*.cache" -o -name "*.glob" -o -name "*.vio" \) -print -delete || true
-	rm -f Makefile.coq .lia.cache
+	+@$(MAKE) -f Makefile.coq clean
+	@# Make sure not to enter the `_opam` folder.
+	find [a-z]*/ \( -name "*.d" -o -name "*.vo" -o -name "*.vo[sk]" -o -name "*.aux" -o -name "*.cache" -o -name "*.glob" -o -name "*.vio" \) -print -delete || true
+	rm -f Makefile.coq .lia.cache builddep/*
 .PHONY: clean
 
 # Create Coq Makefile.
 Makefile.coq: _CoqProject Makefile
-	"$(COQBIN)coq_makefile" -f _CoqProject -o Makefile.coq
+	"$(COQBIN)coq_makefile" -f _CoqProject -o Makefile.coq $(EXTRA_COQFILES)
 
 # Install build-dependencies
-build-dep/opam: opam Makefile
-	@echo "# Creating build-dep package."
-	@mkdir -p build-dep
-	@sed <opam -E 's/^(build|install|remove):.*/\1: []/; s/^name: *"(.*)" */name: "\1-builddep"/' >build-dep/opam
-	@fgrep builddep build-dep/opam >/dev/null || (echo "sed failed to fix the package name" && exit 1) # sanity check
-
-build-dep: build-dep/opam phony
-	@# We want opam to not just instal the build-deps now, but to also keep satisfying these
+OPAMFILES=$(wildcard *.opam)
+BUILDDEPFILES=$(addsuffix -builddep.opam, $(addprefix builddep/,$(basename $(OPAMFILES))))
+
+builddep/%-builddep.opam: %.opam Makefile
+	@echo "# Creating builddep package for $<."
+	@mkdir -p builddep
+	@sed <$< -E 's/^(build|install|remove):.*/\1: []/; s/"(.*)"(.*= *version.*)$$/"\1-builddep"\2/;' >$@
+
+builddep-opamfiles: $(BUILDDEPFILES)
+.PHONY: builddep-opamfiles
+
+builddep: builddep-opamfiles
+	@# We want opam to not just install the build-deps now, but to also keep satisfying these
 	@# constraints.  Otherwise, `opam upgrade` may well update some packages to versions
 	@# that are incompatible with our build requirements.
 	@# To achieve this, we create a fake opam package that has our build-dependencies as
 	@# dependencies, but does not actually install anything itself.
-	@echo "# Installing build-dep package."
-	@opam install $(OPAMFLAGS) build-dep/
+	@echo "# Installing builddep packages."
+	@opam install $(OPAMFLAGS) $(BUILDDEPFILES)
+.PHONY: builddep
 
-# Some files that do *not* need to be forwarded to Makefile.coq
-Makefile: ;
-_CoqProject: ;
-opam: ;
+# Backwards compatibility target
+build-dep: builddep
+.PHONY: build-dep
 
-# Phony wildcard targets
-phony: ;
-.PHONY: phony
+# Some files that do *not* need to be forwarded to Makefile.coq.
+# ("::" lets Makefile.local overwrite this.)
+Makefile Makefile.local _CoqProject $(OPAMFILES):: ;
diff --git a/opam b/coq-actris.opam
similarity index 54%
rename from opam
rename to coq-actris.opam
index 135c8a3725b9b53f4761220912cfd23181610d07..56c63871177c2ddab1e000eba64c8eb9eec5e70a 100644
--- a/opam
+++ b/coq-actris.opam
@@ -1,13 +1,13 @@
-opam-version: "1.2"
-name: "coq-actris"
+opam-version: "2.0"
 maintainer: "Robbert Krebbers"
 authors: "Jonas Kastberg Hinrichsen, Daniël Louwrink, Jesper Bengtson, Robbert Krebbers"
 license: "BSD"
 bug-reports: "https://gitlab.mpi-sws.org/iris/actris/issues"
-dev-repo: "https://gitlab.mpi-sws.org/iris/actris.git"
-build: [make "-j%{jobs}%"]
-install: [make "install"]
-remove: [ "sh" "-c" "rm -rf '%{lib}%/coq/user-contrib/actris" ]
+dev-repo: "git+https://gitlab.mpi-sws.org/iris/actris.git"
+
 depends: [
-  "coq-iris-heap-lang" { (= "dev.2021-12-08.1.8699ad5a") | (= "dev") }
+  "coq-iris-heap-lang" { (= "dev.2021-12-09.1.f52f9f6a") | (= "dev") }
 ]
+
+build: [make "-j%{jobs}%"]
+install: [make "install"]