diff --git a/.github/actions/check-compat-bounds/action.yml b/.github/actions/check-compat-bounds/action.yml
index 05c8a16..1d9ac78 100644
--- a/.github/actions/check-compat-bounds/action.yml
+++ b/.github/actions/check-compat-bounds/action.yml
@@ -44,7 +44,12 @@ runs:
         esac
 
         if [ "$run_check" = "true" ]; then
-          julia --color=yes "$SCRIPT_PATH" "$WORKSPACE_ROOT"
+          # The script reads the registries through RegistryInstances, so give it a
+          # throwaway environment of its own rather than the workspace being checked.
+          script_env="$(mktemp -d)"
+          julia --color=yes --project="$script_env" -e \
+            'using Pkg; Pkg.add(Pkg.PackageSpec(; name = "RegistryInstances", version = "0.1"))'
+          julia --color=yes --project="$script_env" "$SCRIPT_PATH" "$WORKSPACE_ROOT"
         else
           echo "Skipping compat-bounds check (mode=$MODE, actor=${GITHUB_ACTOR:-unset})."
         fi
diff --git a/.github/actions/check-compat-bounds/check_compat_bounds.jl b/.github/actions/check-compat-bounds/check_compat_bounds.jl
index fd14df9..479b22e 100644
--- a/.github/actions/check-compat-bounds/check_compat_bounds.jl
+++ b/.github/actions/check-compat-bounds/check_compat_bounds.jl
@@ -16,6 +16,10 @@
 #   workspace-root : defaults to pwd()
 
 using Pkg
+# The registry abstraction is an implementation detail of `Pkg` whose signatures
+# change between Julia minor versions. RegistryInstances exports the same names
+# as public API under semver, so read the registries through it instead.
+using RegistryInstances: reachable_registries, registry_info
 using TOML
 
 function parse_args(args)
@@ -128,10 +132,10 @@ end
 
 function registry_versions(uuid::Base.UUID)
     versions = VersionNumber[]
-    for reg in Pkg.Registry.reachable_registries()
+    for reg in reachable_registries()
         entry = get(reg.pkgs, uuid, nothing)
         entry === nothing && continue
-        info = Pkg.Registry.registry_info(entry)
+        info = registry_info(entry)
         for (v, vinfo) in info.version_info
             vinfo.yanked && continue
             push!(versions, v)