diff --git a/src/Operations.jl b/src/Operations.jl
index f3ddd02e6e..2dc60dec46 100644
--- a/src/Operations.jl
+++ b/src/Operations.jl
@@ -235,7 +235,7 @@ function fixups_from_projectfile!(ctx::Context)
             # pkg.exts = p.exts # TODO: STDLIBS_BY_VERSION doesn't record this
             # pkg.entryfile = p.entryfile # TODO: STDLIBS_BY_VERSION doesn't record this
             for (name, _) in pkg.weakdeps
-                if !haskey(p.deps, name)
+                if !(name in p.deps)
                     delete!(pkg.deps, name)
                 end
             end
diff --git a/test/historical_stdlib_version.jl b/test/historical_stdlib_version.jl
index e19574155d..7720e2a91f 100644
--- a/test/historical_stdlib_version.jl
+++ b/test/historical_stdlib_version.jl
@@ -255,6 +255,11 @@ isolate(loaded_depot=true) do
             end
         end
 
+        @testset "Old Pkg add regression" begin
+            Pkg.activate(temp=true)
+            Pkg.add(; name="Pkg", julia_version=v"1.11")
+        end
+
         @testset "Stdlib add" begin
             Pkg.activate(temp=true)
             # Stdlib add (current julia version)