diff --git a/libraries/stdlib/js/irRuntime/generated/_ArraysJs.kt b/libraries/stdlib/js/irRuntime/generated/_ArraysJs.kt
index f0617b7c9a4..869cd739670 100644
--- a/libraries/stdlib/js/irRuntime/generated/_ArraysJs.kt
+++ b/libraries/stdlib/js/irRuntime/generated/_ArraysJs.kt
@@ -1015,21 +1015,30 @@ public actual operator fun <T> Array<out T>.plus(elements: Collection<T>): Array
  * Returns an array containing all elements of the original array and then all elements of the given [elements] collection.
  */
 public actual operator fun ByteArray.plus(elements: Collection<Byte>): ByteArray {
-    return fillFromCollection(this.copyOf(size + elements.size), this.size, elements)
+    var index = size
+    val result = this.copyOf(size + elements.size)
+    for (element in elements) result[index++] = element
+    return result
 }
 
 /**
  * Returns an array containing all elements of the original array and then all elements of the given [elements] collection.
  */
 public actual operator fun ShortArray.plus(elements: Collection<Short>): ShortArray {
-    return fillFromCollection(this.copyOf(size + elements.size), this.size, elements)
+    var index = size
+    val result = this.copyOf(size + elements.size)
+    for (element in elements) result[index++] = element
+    return result
 }
 
 /**
  * Returns an array containing all elements of the original array and then all elements of the given [elements] collection.
  */
 public actual operator fun IntArray.plus(elements: Collection<Int>): IntArray {
-    return fillFromCollection(this.copyOf(size + elements.size), this.size, elements)
+    var index = size
+    val result = this.copyOf(size + elements.size)
+    for (element in elements) result[index++] = element
+    return result
 }
 
 /**
@@ -1043,14 +1052,20 @@ public actual operator fun LongArray.plus(elements: Collection<Long>): LongArray
  * Returns an array containing all elements of the original array and then all elements of the given [elements] collection.
  */
 public actual operator fun FloatArray.plus(elements: Collection<Float>): FloatArray {
-    return fillFromCollection(this.copyOf(size + elements.size), this.size, elements)
+    var index = size
+    val result = this.copyOf(size + elements.size)
+    for (element in elements) result[index++] = element
+    return result
 }
 
 /**
  * Returns an array containing all elements of the original array and then all elements of the given [elements] collection.
  */
 public actual operator fun DoubleArray.plus(elements: Collection<Double>): DoubleArray {
-    return fillFromCollection(this.copyOf(size + elements.size), this.size, elements)
+    var index = size
+    val result = this.copyOf(size + elements.size)
+    for (element in elements) result[index++] = element
+    return result
 }
 
 /**
@@ -1064,7 +1079,10 @@ public actual operator fun BooleanArray.plus(elements: Collection<Boolean>): Boo
  * Returns an array containing all elements of the original array and then all elements of the given [elements] collection.
  */
 public actual operator fun CharArray.plus(elements: Collection<Char>): CharArray {
-    return fillFromCollection(this.copyOf(size + elements.size), this.size, elements)
+    var index = size
+    val result = this.copyOf(size + elements.size)
+    for (element in elements) result[index++] = element
+    return result
 }
 
 /**
diff --git a/libraries/stdlib/js/irRuntime/kotlinHacks.kt b/libraries/stdlib/js/irRuntime/kotlinHacks.kt
index 45eb42cc97b..a3b7e29fb76 100644
--- a/libraries/stdlib/js/irRuntime/kotlinHacks.kt
+++ b/libraries/stdlib/js/irRuntime/kotlinHacks.kt
@@ -66,13 +66,6 @@ internal fun <T> arrayPlusCollection(array: dynamic, collection: Collection<T>):
     return result
 }
 
-internal fun <T> fillFromCollection(dst: dynamic, startIndex: Int, collection: Collection<T>): dynamic {
-    var index = startIndex
-    val arr = dst.unsafeCast<Array<T>>()
-    for (element in collection) arr[index++] = element
-    return dst
-}
-
 internal inline fun copyArrayType(from: dynamic, to: dynamic) {
     if (from.`$type$` !== undefined) {
         to.`$type$` = from.`$type$`
diff --git a/libraries/tools/kotlin-stdlib-gen/src/templates/Arrays.kt b/libraries/tools/kotlin-stdlib-gen/src/templates/Arrays.kt
index 5849f683d28..9ca1227f775 100644
--- a/libraries/tools/kotlin-stdlib-gen/src/templates/Arrays.kt
+++ b/libraries/tools/kotlin-stdlib-gen/src/templates/Arrays.kt
@@ -532,8 +532,26 @@ object ArrayOps : TemplateGroupBase() {
             when (primitive) {
                 null, PrimitiveType.Boolean, PrimitiveType.Long ->
                     body { "return arrayPlusCollection(this, elements)" }
-                else ->
-                    body { "return fillFromCollection(this.copyOf(size + elements.size), this.size, elements)" }
+                else -> {
+                    on(Backend.Legacy) {
+                        body {
+                            "return fillFromCollection(this.copyOf(size + elements.size), this.size, elements)"
+                        }
+                    }
+                    on(Backend.IR) {
+                        // Don't use fillFromCollection because it treats arrays
+                        // as `dynamic` but we need to concrete types to perform
+                        // unboxing of collections elements
+                        body {
+                            """
+                            var index = size
+                            val result = this.copyOf(size + elements.size)
+                            for (element in elements) result[index++] = element
+                            return result
+                            """
+                        }
+                    }
+                }
             }
         }
         on(Platform.Native) {