diff --git a/Project.toml b/Project.toml
index be01bf2..31e166c 100644
--- a/Project.toml
+++ b/Project.toml
@@ -4,9 +4,11 @@ version = "1.0.0"
 
 [deps]
 JuliaSyntax = "70703baa-626e-46a2-a12c-08ffd08c73b4"
+Preferences = "21216c6a-2e73-6563-6e65-726566657250"
 
 [compat]
 JuliaSyntax = "0.4.10"
+Preferences = "1"
 
 [extras]
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
diff --git a/juliac/.gitignore b/juliac/.gitignore
index ffd8f01..2ba9a79 100644
--- a/juliac/.gitignore
+++ b/juliac/.gitignore
@@ -1 +1,2 @@
+/Manifest.toml
 /runicc
diff --git a/juliac/Makefile b/juliac/Makefile
index b22f24e..99300e8 100644
--- a/juliac/Makefile
+++ b/juliac/Makefile
@@ -1,26 +1,18 @@
 JULIA ?= /opt/julia/julia-c/bin/julia
 JULIAC ?= $(shell $(JULIA) -e 'print(normpath(joinpath(Sys.BINDIR, Base.DATAROOTDIR, "julia", "juliac.jl")))')
-RUNIC_SRCFILES := $(wildcard ../src/*.jl)
 
-runicc: runicc.jl $(RUNIC_SRCFILES) invalidate-precompile-cache
-	$(JULIA) $(JULIAC) --output-exe $@ --trim=unsafe-warn $<
+RUNIC_FILES := $(wildcard ../src/*.jl) ../Project.toml
 
-clean:
-	rm runicc
+runicc: runicc.jl Project.toml Manifest.toml $(RUNIC_FILES)
+	$(JULIA) --project=. $(JULIAC) --output-exe $@ --trim=unsafe-warn $<
+
+Manifest.toml: Project.toml ../Project.toml
+	$(JULIA) --project=. -e 'using Pkg; Pkg.instantiate()'
 
-# Prune cached precompile files for Runic. This is needed because there are
-# (compile time) branches in the Runic source code which depends on whether
-# Runic is compiled or not. It looks like juliac will use existing cache files
-# but not produce any so there is no need to prune them again after compilation
-# to force regular usage to recompile.
-invalidate-precompile-cache:
-	$(JULIA) -e ' \
-		ji = Base.compilecache_path(Base.PkgId(Base.UUID("62bfec6d-59d7-401d-8490-b29ee721c001"), "Runic")); \
-		if ji !== nothing; \
-			isfile(ji) && (@info "Deleting precompile file $$(ji)"; rm(ji)); \
-			so = splitext(ji)[1] * "." * Base.BinaryPlatforms.platform_dlext(); \
-			isfile(so) && (@info "Deleting pkgimage file $$(so)"; rm(so)); \
-		end'
+clean:
+	-rm -f runicc Manifest.toml
 
+print-%:
+	@echo '$*=$($*)'
 
-.PHONY: invalidate-precompile-cache clean
+.PHONY: clean
diff --git a/src/main.jl b/src/main.jl
index e275ddd..16440b8 100644
--- a/src/main.jl
+++ b/src/main.jl
@@ -7,13 +7,8 @@ else
 end
 
 # Check whether we are compiling with juliac
-# TODO: I thought juliac would never use existing pkgimages but looks like it does so this
-# isn't reliable... Existing cache files are pruned in the Makefile for now.
-const juliac = let opts = Base.JLOptions()
-    hasfield(typeof(opts), :trim) &&
-        getfield(opts, :trim) != 0 &&
-        Base.generating_output()
-end
+using Preferences: @load_preference
+const juliac = @load_preference("juliac", false)
 
 @static if juliac
     stderr() = Core.stderr