diff --git a/.gitignore b/.gitignore
index 23ef4c4425ad44d7a61fc693ab762e57f0981f5e..11026597a5192e0338cd5674dd0c9e2beca63f35 100644
--- a/.gitignore
+++ b/.gitignore
@@ -13,7 +13,7 @@
 *~
 *.bak
 .coq-native/
-build-dep/
+builddep/
 Makefile.coq
 Makefile.coq.conf
 _opam
diff --git a/Makefile b/Makefile
index 331cb03f841de9ffc5711e876acd402e4816fb87..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 exercises solutions \( -name "*.d" -o -name "*.vo" -o -name "*.vo[sk]" -o -name "*.aux" -o -name "*.cache" -o -name "*.glob" -o -name "*.vio" \) -print -delete || true
-	rm -f Makefile.coq .lia.cache
+	+@$(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-lambda-rust.opam
similarity index 96%
rename from opam
rename to coq-lambda-rust.opam
index bfd16df3d1dfe6b057b2c7235bb2786658a0e7dd..5e603258b59fd5934af5df3b34e532394b8a539a 100644
--- a/opam
+++ b/coq-lambda-rust.opam
@@ -1,5 +1,4 @@
 opam-version: "2.0"
-name: "coq-lambda-rust"
 maintainer: "Ralf Jung <jung@mpi-sws.org>"
 authors: "The RustBelt Team"
 license: "BSD"