diff --git a/base/precompilation.jl b/base/precompilation.jl
index 4efd35836a29d..736fc3b27fb0e 100644
--- a/base/precompilation.jl
+++ b/base/precompilation.jl
@@ -26,6 +26,9 @@ struct ExplicitEnv
 end
 
 function ExplicitEnv(envpath::String=Base.active_project())
+    if !isfile(envpath)
+        error("expected a project file at $(repr(envpath))")
+    end
     envpath = abspath(envpath)
     project_d = parsed_toml(envpath)
 
@@ -51,6 +54,11 @@ function ExplicitEnv(envpath::String=Base.active_project())
         end
     end
 
+    # A package in both deps and weakdeps is in fact only a weakdep
+    for (name, _) in project_weakdeps
+        delete!(project_deps, name)
+    end
+
     project_extensions = Dict{String, Vector{UUID}}()
     # Collect all extensions of the project
     for (name, triggers::Union{String, Vector{String}}) in get(Dict{String, Any}, project_d, "extensions")::Dict{String, Any}