diff --git a/stdlib/public/core/ArrayBufferType.swift b/stdlib/public/core/ArrayBufferType.swift
index 560ae923181..40fa99e32a1 100644
--- a/stdlib/public/core/ArrayBufferType.swift
+++ b/stdlib/public/core/ArrayBufferType.swift
@@ -160,12 +160,12 @@ extension _ArrayBufferType {
       var i = newValues.startIndex
       for j in subRange {
         elements[j] = newValues[i]
-        i = i.successor()
+        i._successorInPlace()
       }
       // Initialize the hole left by sliding the tail forward
       for j in oldTailIndex..<newTailIndex {
         (elements + j).initialize(newValues[i])
-        i = i.successor()
+        i._successorInPlace()
       }
       _expectEnd(i, newValues)
     }
@@ -175,8 +175,8 @@ extension _ArrayBufferType {
       var j = newValues.startIndex
       for _ in 0..<newCount {
         elements[i] = newValues[j]
-        i = i.successor()
-        j = j.successor()
+        i._successorInPlace()
+        j._successorInPlace()
       }
       _expectEnd(j, newValues)
 
diff --git a/stdlib/public/core/Collection.swift b/stdlib/public/core/Collection.swift
index cf3c136291a..f3519b3a779 100644
--- a/stdlib/public/core/Collection.swift
+++ b/stdlib/public/core/Collection.swift
@@ -728,8 +728,8 @@ internal func _writeBackMutableSlice<
     newElementIndex != newElementsEndIndex {
 
     self_[selfElementIndex] = slice[newElementIndex]
-    selfElementIndex = selfElementIndex.successor()
-    newElementIndex = newElementIndex.successor()
+    selfElementIndex._successorInPlace()
+    newElementIndex._successorInPlace()
   }
 
   _precondition(
diff --git a/stdlib/public/core/ContiguousArrayBuffer.swift b/stdlib/public/core/ContiguousArrayBuffer.swift
index e3125b11a0b..7c5696560ee 100644
--- a/stdlib/public/core/ContiguousArrayBuffer.swift
+++ b/stdlib/public/core/ContiguousArrayBuffer.swift
@@ -609,8 +609,8 @@ internal func _copyCollectionToNativeArrayBuffer<
   for _ in 0..<count {
     // FIXME(performance): use _initializeTo().
     p.initialize(source[i])
-    i = i.successor()
-    p = p.successor()
+    i._successorInPlace()
+    p._successorInPlace()
   }
   _expectEnd(i, source)
   return result
diff --git a/stdlib/public/core/Existential.swift b/stdlib/public/core/Existential.swift
index 9ca60b7b72b..06a44c4ad21 100644
--- a/stdlib/public/core/Existential.swift
+++ b/stdlib/public/core/Existential.swift
@@ -44,7 +44,7 @@ internal struct _CollectionOf<
     return AnyGenerator {
       () -> T? in
       if _fastPath(index != self.endIndex) {
-        index = index.successor()
+        index._successorInPlace()
         return self._subscriptImpl(index)
       }
       return nil
diff --git a/stdlib/public/core/HashedCollections.swift.gyb b/stdlib/public/core/HashedCollections.swift.gyb
index cffd0c65a97..098c08fd1b6 100644
--- a/stdlib/public/core/HashedCollections.swift.gyb
+++ b/stdlib/public/core/HashedCollections.swift.gyb
@@ -1231,7 +1231,7 @@ public func == <Key : Equatable, Value : Equatable>(
 
     let endIndex = lhsNative.endIndex
     for var index = lhsNative.startIndex; index != endIndex;
-        index = index.successor() {
+        index._successorInPlace() {
       let (key, value) = lhsNative.assertingGet(index)
       let optRhsValue: AnyObject? =
         rhsCocoa.maybeGet(_bridgeToObjectiveCUnconditional(key))
@@ -2390,7 +2390,7 @@ final internal class _Native${Self}StorageKeyNSEnumerator<
       return nil
     }
     let bridgedKey: AnyObject = nativeStorageOwner._getBridgedKey(nextIndex)
-    nextIndex = nextIndex.successor()
+    nextIndex._successorInPlace()
     return bridgedKey
   }
 
@@ -2415,7 +2415,7 @@ final internal class _Native${Self}StorageKeyNSEnumerator<
     // Return only a single element so that code can start iterating via fast
     // enumeration, terminate it, and continue via NSEnumerator.
     let bridgedKey: AnyObject = nativeStorageOwner._getBridgedKey(nextIndex)
-    nextIndex = nextIndex.successor()
+    nextIndex._successorInPlace()
 
     let unmanagedObjects = _UnmanagedAnyObjectArray(objects)
     unmanagedObjects[0] = bridgedKey
@@ -2767,7 +2767,7 @@ final internal class _Native${Self}StorageOwner<${TypeParametersDecl}>
       let bridgedKey: AnyObject = _getBridgedKey(currIndex)
       unmanagedObjects[i] = bridgedKey
       ++stored
-      currIndex = currIndex.successor()
+      currIndex._successorInPlace()
     }
     theState.extra.0 = CUnsignedLong(currIndex.offset)
     state.memory = theState
@@ -3970,7 +3970,7 @@ internal struct ${Self}MirrorPosition<${TypeParametersDecl}> {
 
   internal mutating func successor() {
     _intPos = _intPos + 1
-    ${Self}Pos = ${Self}Pos.successor()
+    ${Self}Pos._successorInPlace()
   }
 
 }
diff --git a/stdlib/public/core/Index.swift b/stdlib/public/core/Index.swift
index 708cc390f6d..526d91a78ee 100644
--- a/stdlib/public/core/Index.swift
+++ b/stdlib/public/core/Index.swift
@@ -216,7 +216,7 @@ extension ForwardIndexType {
     var p = self
     var i : Distance = 0
     while i != n {
-      p = p.successor()
+      p._successorInPlace()
       i = i + 1
     }
     return p
@@ -232,7 +232,7 @@ extension ForwardIndexType {
     var i : Distance = 0
     while i != n {
       if p == limit { break }
-      p = p.successor()
+      p._successorInPlace()
       i = i + 1
     }
     return p
@@ -254,7 +254,7 @@ extension ForwardIndexType {
     var count: Distance = 0
     while p != end {
       count += 1
-      p = p.successor()
+      p._successorInPlace()
     }
     return count
   }
diff --git a/stdlib/public/core/Sort.swift.gyb b/stdlib/public/core/Sort.swift.gyb
index 7288fdc9e87..67a7e7ed5c9 100644
--- a/stdlib/public/core/Sort.swift.gyb
+++ b/stdlib/public/core/Sort.swift.gyb
@@ -56,7 +56,7 @@ func _insertionSort<
 
     // One element is trivially already-sorted, thus pre-increment
     // Continue until the sorted elements cover the whole sequence
-    sortedEnd = sortedEnd.successor()
+    sortedEnd._successorInPlace()
     while sortedEnd != range.endIndex {
       // get the first unsorted element
       let x: C.Generator.Element = elements[sortedEnd]
@@ -81,7 +81,7 @@ func _insertionSort<
         // Plop x into position
         elements[i] = x
       }
-      sortedEnd = sortedEnd.successor()
+      sortedEnd._successorInPlace()
     }
   }
 }
diff --git a/stdlib/public/core/StringCharacterView.swift b/stdlib/public/core/StringCharacterView.swift
index 57a0f3c4b32..a6d3e40d5c4 100644
--- a/stdlib/public/core/StringCharacterView.swift
+++ b/stdlib/public/core/StringCharacterView.swift
@@ -143,9 +143,9 @@ extension String.CharacterView : CollectionType {
 
       var gcb0 = graphemeClusterBreakProperty.getPropertyRawValue(
           unicodeScalars[start].value)
-      start = start.successor()
+      start._successorInPlace()
 
-      for ; start != end; start = start.successor() {
+      for ; start != end; start._successorInPlace() {
         // FIXME(performance): consider removing this "fast path".  A branch
         // that is hard to predict could be worse for performance than a few
         // loads from cache to fetch the property 'gcb1'.
diff --git a/stdlib/public/core/StringLegacy.swift b/stdlib/public/core/StringLegacy.swift
index 55c5862ba87..7f2b9e0359d 100644
--- a/stdlib/public/core/StringLegacy.swift
+++ b/stdlib/public/core/StringLegacy.swift
@@ -158,7 +158,7 @@ extension String {
     let rng = unicodeScalars
     var startIndex = rng.startIndex
     for _ in 0..<start {
-      startIndex = startIndex.successor()
+      startIndex._successorInPlace()
     }
     return String(rng[startIndex..<rng.endIndex])
   }