diff --git a/libraries/stdlib/src/kotlin/collections/MutableCollections.kt b/libraries/stdlib/src/kotlin/collections/MutableCollections.kt
index bc48f18b874..f2e50db6c87 100644
--- a/libraries/stdlib/src/kotlin/collections/MutableCollections.kt
+++ b/libraries/stdlib/src/kotlin/collections/MutableCollections.kt
@@ -3,6 +3,11 @@
 
 package kotlin
 
+@Deprecated("Use property `size` instead", ReplaceWith("this.size"))
+public inline fun Collection<*>.size() = size
+@Deprecated("Use property `size` instead", ReplaceWith("this.size"))
+public inline fun Map<*, *>.size() = size
+
 /**
  * Adds the specified [element] to this mutable collection.
  */