diff --git a/src/RegistryTools.jl b/src/RegistryTools.jl
index 6a10ae3..16d0f2e 100644
--- a/src/RegistryTools.jl
+++ b/src/RegistryTools.jl
@@ -11,6 +11,14 @@ using Pkg: Pkg, TOML, GitTools
 using UUIDs
 
 const DEFAULT_REGISTRY_URL = "https://github.com/JuliaRegistries/General"
+const PKG_HAS_WEAK = hasfield(Pkg.Types.Project, :_deps_weak)
+
+function __init__()
+    if !PKG_HAS_WEAK
+        @warn "Running Registrator on a Julia version that does not support weak dependencies. \
+              Weak dependencies will not be registered."
+    end
+end
 
 include("Compress.jl")
 include("builtin_pkgs.jl")
diff --git a/src/register.jl b/src/register.jl
index b521cbb..9e5f054 100644
--- a/src/register.jl
+++ b/src/register.jl
@@ -47,8 +47,6 @@ for the project file in that tree and a hash string for the tree.
 #     end
 # end
 
-const PKG_HAS_WEAK = hasfield(Pkg.Types.Project, :_deps_weak)
-
 function getdeps(pkg)
     if PKG_HAS_WEAK
         return merge(pkg.deps, pkg._deps_weak)