diff --git a/test/stdlib/KVOKeyPaths.swift b/test/stdlib/KVOKeyPaths.swift
index 00dbc67dc1f3a..26a410c60db5f 100644
--- a/test/stdlib/KVOKeyPaths.swift
+++ b/test/stdlib/KVOKeyPaths.swift
@@ -215,6 +215,6 @@ testObjectForOptionalKeyPath.optionalObject = nil
 testObjectForOptionalKeyPath.optionalObject = "foo"
 
 // CHECK-51-LABEL: observe keyPath with optional value
-// CHECK-51-NEXT: oldValue = Optional(nil), newValue = {{Optional\(nil\)|nil}}
-// CHECK-51-NEXT: oldValue = Optional(nil), newValue = {{Optional\(nil\)|nil}}
-// CHECK-51-NEXT: oldValue = Optional(nil), newValue = Optional(Optional("foo"))
+// CHECK-51-NEXT: oldValue = {{Optional\(nil\)|nil}}, newValue = {{Optional\(nil\)|nil}}
+// CHECK-51-NEXT: oldValue = {{Optional\(nil\)|nil}}, newValue = {{Optional\(nil\)|nil}}
+// CHECK-51-NEXT: oldValue = {{Optional\(nil\)|nil}}, newValue = Optional(Optional("foo"))
diff --git a/validation-test/stdlib/ArrayTrapsObjC.swift b/validation-test/stdlib/ArrayTrapsObjC.swift
index 9da81f0d09019..8a4ea3e1cc0ed 100644
--- a/validation-test/stdlib/ArrayTrapsObjC.swift
+++ b/validation-test/stdlib/ArrayTrapsObjC.swift
@@ -83,6 +83,18 @@ ArrayTraps.test("bounds_with_downcast")
   _ = da[2]
 }
 
+func hasBackdeployedConcurrencyRuntime() -> Bool {
+  // If the stdlib we've loaded predates Swift 5.5, then we're running on a back
+  // deployed concurrency runtime, which has the side effect of disabling
+  // regular runtime exclusivity checks.
+  //
+  // This makes the two tests below fall back to older, higher-level exclusivity
+  // checks in the stdlib, which will still trap, but with a different message.
+  if #available(SwiftStdlib 5.5, *) { return false } // recent enough production stdlib
+  if #available(SwiftStdlib 9999, *) { return false } // dev stdlib
+  return true
+}
+
 var ArraySemanticOptzns = TestSuite("ArraySemanticOptzns" + testSuiteSuffix)
 
 class BaseClass {
@@ -131,8 +143,11 @@ ArraySemanticOptzns.test("inout_rule_violated_isNativeBuffer")
   .skip(.custom(
     { _isFastAssertConfiguration() },
     reason: "this trap is not guaranteed to happen in -Ounchecked"))
-  .crashOutputMatches(_isDebugAssertConfiguration() ?
-    "Fatal access conflict detected." : "")
+  .crashOutputMatches(
+    !_isDebugAssertConfiguration() ? ""
+    : hasBackdeployedConcurrencyRuntime() ? "inout rules were violated"
+    : "Fatal access conflict detected."
+  )
   .code {
   let v = ViolateInoutSafetySwitchToObjcBuffer()
   expectCrashLater()
@@ -174,8 +189,11 @@ ArraySemanticOptzns.test("inout_rule_violated_needsElementTypeCheck")
   .skip(.custom(
     { _isFastAssertConfiguration() },
     reason: "this trap is not guaranteed to happen in -Ounchecked"))
-  .crashOutputMatches(_isDebugAssertConfiguration() ?
-    "Fatal access conflict detected." : "")
+  .crashOutputMatches(
+    !_isDebugAssertConfiguration() ? ""
+    : hasBackdeployedConcurrencyRuntime() ? "inout rules were violated"
+    : "Fatal access conflict detected."
+  )
   .code {
   let v = ViolateInoutSafetyNeedElementTypeCheck()
   expectCrashLater()
diff --git a/validation-test/stdlib/SetOperations.swift.gyb b/validation-test/stdlib/SetOperations.swift.gyb
index 57a6e85fbf137..47cca4ddb812a 100644
--- a/validation-test/stdlib/SetOperations.swift.gyb
+++ b/validation-test/stdlib/SetOperations.swift.gyb
@@ -248,66 +248,6 @@ suite.test("symmetricDifference.${inputKind}.${argumentKind}") {
 %   end
 % end
 
-% for inputKind, inputGenerator in inputKinds.items():
-%   for argumentKind, argumentGenerator in argumentKinds.items():
-%     needsCocoa = inputKind == "cocoa" or argumentKind == "cocoa"
-%     if needsCocoa:
-#if _runtime(_ObjC)
-%     end
-suite.test("formIntersection.${inputKind}.${argumentKind}") {
-  var a = ${inputGenerator}(0 ..< 10, identity: 1)
-  let b = ${argumentGenerator}(5 ..< 15, identity: 2)
-  a.formSymmetricDifference(b)
-  expectTrue(isNativeSet(a))
-  expectEqual(a.count, 10)
-  // Check the resulting items and that they come from the correct input set.
-  for v in 5 ..< 10 {
-    expectFalse(a.contains(Value(v)), "Found \(v) in result")
-  }
-  for v in Array(0 ..< 5) + Array(10 ..< 15) {
-    guard let i = a.firstIndex(of: Value(v)) else {
-      expectTrue(false, "Could not find \(v) in result")
-      continue
-    }
-    expectEqual(a[i].identity, v < 5 ? 1 : 2)
-  }
-}
-%     if needsCocoa:
-#endif
-%     end
-%   end
-% end
-
-% for inputKind, inputGenerator in inputKinds.items():
-%   for argumentKind, argumentGenerator in argumentKinds.items():
-%     needsCocoa = inputKind == "cocoa" or argumentKind == "cocoa"
-%     if needsCocoa:
-#if _runtime(_ObjC)
-%     end
-suite.test("symmetricDifference.${inputKind}.${argumentKind}") {
-  let a = ${inputGenerator}(0 ..< 10, identity: 1)
-  let b = ${argumentGenerator}(5 ..< 15, identity: 2)
-  let c = a.symmetricDifference(b)
-  expectTrue(isNativeSet(c))
-  expectEqual(c.count, 10)
-  // Check the resulting items and that they come from the correct input set.
-  for v in 5 ..< 10 {
-    expectFalse(c.contains(Value(v)), "Found \(v) in result")
-  }
-  for v in Array(0 ..< 5) + Array(10 ..< 15) {
-    guard let i = c.firstIndex(of: Value(v)) else {
-      expectTrue(false, "Could not find \(v) in result")
-      continue
-    }
-    expectEqual(c[i].identity, v < 5 ? 1 : 2)
-  }
-}
-%     if needsCocoa:
-#endif
-%     end
-%   end
-% end
-
 % for inputKind, inputGenerator in inputKinds.items():
 %   for argumentKind, argumentGenerator in argumentKinds.items():
 %     needsCocoa = inputKind == "cocoa" or argumentKind == "cocoa"