diff --git a/packages/associative/src/merge-apply.ts b/packages/associative/src/merge-apply.ts
index 044d92b0e5..8d70f70012 100644
--- a/packages/associative/src/merge-apply.ts
+++ b/packages/associative/src/merge-apply.ts
@@ -1,7 +1,7 @@
 import type { Fn, IObjectOf } from "@thi.ng/api";
 import { isFunction } from "@thi.ng/checks/is-function";
 import { isIllegalKey } from "@thi.ng/checks/is-proto-path";
-import { copy } from "./utils";
+import { copy, copyObj } from "./utils";
 
 /**
  * Similar to {@link mergeApplyObj}, but for ES6 Maps instead of plain objects.
@@ -51,7 +51,7 @@ export const mergeApplyMap = <K, V>(
 export const mergeApplyObj = <V>(
     src: IObjectOf<V>,
     xs: IObjectOf<V | Fn<V, V>>
-) => meldApplyObj({ ...src }, xs);
+) => meldApplyObj(copyObj(src), xs);
 
 /**
  * Mutable version of {@link mergeApplyObj}. Returns modified `src`
diff --git a/packages/associative/src/merge-with.ts b/packages/associative/src/merge-with.ts
index 3cfc7b9fe7..3304a63148 100644
--- a/packages/associative/src/merge-with.ts
+++ b/packages/associative/src/merge-with.ts
@@ -1,6 +1,6 @@
 import type { Fn2, IObjectOf, Nullable } from "@thi.ng/api";
 import { isIllegalKey } from "@thi.ng/checks/is-proto-path";
-import { copy } from "./utils";
+import { copy, copyObj } from "./utils";
 
 export const mergeMapWith = <K, V>(
     f: Fn2<V, V, V>,
@@ -35,7 +35,7 @@ export const mergeObjWith = <T>(
     f: Fn2<T, T, T>,
     dest: IObjectOf<T>,
     ...xs: Nullable<IObjectOf<T>>[]
-) => meldObjWith(f, { ...dest }, ...xs);
+) => meldObjWith(f, copyObj(dest), ...xs);
 
 /**
  * Mutable version of {@link mergeObjWith}. Returns modified `dest`
diff --git a/packages/associative/src/sparse-set.ts b/packages/associative/src/sparse-set.ts
index 33035006eb..dd8a574258 100644
--- a/packages/associative/src/sparse-set.ts
+++ b/packages/associative/src/sparse-set.ts
@@ -42,7 +42,7 @@ export abstract class ASparseSet<T extends UIntArray>
         return __private.get(this)!.n;
     }
 
-    get capacity() {
+    get capacity(): number {
         return __private.get(this)!.dense.length;
     }
 
diff --git a/packages/associative/src/utils.ts b/packages/associative/src/utils.ts
index e45a5be1da..273119838b 100644
--- a/packages/associative/src/utils.ts
+++ b/packages/associative/src/utils.ts
@@ -1,6 +1,7 @@
 import type { Pair } from "@thi.ng/api";
 import { implementsFunction } from "@thi.ng/checks/implements-function";
 import { isMap } from "@thi.ng/checks/is-map";
+import { isIllegalKey } from "@thi.ng/checks/is-proto-path";
 import { isSet } from "@thi.ng/checks/is-set";
 
 export const empty = (x: any, ctor: Function) =>
@@ -13,6 +14,14 @@ export const copy = (x: any, ctor: Function) =>
         ? x.copy()
         : new (x[Symbol.species] || ctor)(x);
 
+export const copyObj = (x: any) => {
+    const res: any = {};
+    for (let k in x) {
+        !isIllegalKey(k) && (res[k] = x[k]);
+    }
+    return res;
+};
+
 export const first = <T>(x: Iterable<T>) => x[Symbol.iterator]().next().value;
 
 export const objValues = (src: any) => {