diff --git a/lib/AST/NameLookup.cpp b/lib/AST/NameLookup.cpp
index 4f785711cf9f1..99a0310aa1c58 100644
--- a/lib/AST/NameLookup.cpp
+++ b/lib/AST/NameLookup.cpp
@@ -3630,7 +3630,17 @@ NominalTypeDecl *ExtensionDecl::computeExtendedNominal(
   if (nominalTypes.empty())
     return nullptr;
 
-  return nominalTypes[0];
+  auto *result = nominalTypes[0];
+
+  // Tuple extensions are experimental, if the feature isn't enabled let's not
+  // bind this extension at all. This fixes a bunch of crashers that we don't
+  // yet properly handle with the feature enabled.
+  if (isa<BuiltinTupleDecl>(result) &&
+      !ctx.LangOpts.hasFeature(Feature::TupleConformances)) {
+    return nullptr;
+  }
+
+  return result;
 }
 
 NominalTypeDecl *
diff --git a/lib/Sema/TypeCheckDecl.cpp b/lib/Sema/TypeCheckDecl.cpp
index 40ad1ab0cfbbd..b91c36536f66b 100644
--- a/lib/Sema/TypeCheckDecl.cpp
+++ b/lib/Sema/TypeCheckDecl.cpp
@@ -3089,6 +3089,13 @@ ExtendedTypeRequest::evaluate(Evaluator &eval, ExtensionDecl *ext) const {
     return error();
   }
 
+  // Tuple extensions are experimental.
+  if (extendedType->is<TupleType>() &&
+      !ctx.LangOpts.hasFeature(Feature::TupleConformances)) {
+    diags.diagnose(ext, diag::experimental_tuple_extension);
+    return error();
+  }
+
   // Cannot extend function types, metatypes, existentials, etc.
   if (!extendedType->is<TupleType>() &&
       !extendedType->getAnyNominal() &&
diff --git a/lib/Sema/TypeCheckDeclPrimary.cpp b/lib/Sema/TypeCheckDeclPrimary.cpp
index 21835411094e3..5849acc3e7857 100644
--- a/lib/Sema/TypeCheckDeclPrimary.cpp
+++ b/lib/Sema/TypeCheckDeclPrimary.cpp
@@ -3652,10 +3652,8 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       return;
 
     auto &ctx = ED->getASTContext();
-
-    if (!ctx.LangOpts.hasFeature(Feature::TupleConformances)) {
-      ED->diagnose(diag::experimental_tuple_extension);
-    }
+    ASSERT(ctx.LangOpts.hasFeature(Feature::TupleConformances) &&
+           "Extension binding should not have permitted this");
 
     if (!isValidExtendedTypeForTupleExtension(ED)) {
       ED->diagnose(diag::tuple_extension_wrong_type,
diff --git a/validation-test/IDE/crashers/38a36bbe0fc496da.swift b/validation-test/IDE/crashers_fixed/38a36bbe0fc496da.swift
similarity index 51%
rename from validation-test/IDE/crashers/38a36bbe0fc496da.swift
rename to validation-test/IDE/crashers_fixed/38a36bbe0fc496da.swift
index 32668edc7cec7..71248dbbe607b 100644
--- a/validation-test/IDE/crashers/38a36bbe0fc496da.swift
+++ b/validation-test/IDE/crashers_fixed/38a36bbe0fc496da.swift
@@ -1,5 +1,5 @@
 // {"kind":"complete","original":"61e9155a","signature":"swift::ide::CodeCompletionResultBuilder::takeResult()"}
-// RUN: not --crash %target-swift-ide-test -code-completion -batch-code-completion -skip-filecheck -code-completion-diagnostics -source-filename %s
+// RUN: %target-swift-ide-test -code-completion -batch-code-completion -skip-filecheck -code-completion-diagnostics -source-filename %s
 extension ()
 where
   #^^# == <#type#>
diff --git a/validation-test/compiler_crashers_2/0217ed2d301f5d7b.swift b/validation-test/compiler_crashers_2_fixed/0217ed2d301f5d7b.swift
similarity index 71%
rename from validation-test/compiler_crashers_2/0217ed2d301f5d7b.swift
rename to validation-test/compiler_crashers_2_fixed/0217ed2d301f5d7b.swift
index e35344c055316..1ff01f3b60eb5 100644
--- a/validation-test/compiler_crashers_2/0217ed2d301f5d7b.swift
+++ b/validation-test/compiler_crashers_2_fixed/0217ed2d301f5d7b.swift
@@ -1,5 +1,5 @@
 // {"kind":"typecheck","original":"679d3d53","signature":"(anonymous namespace)::PrintAST::visit(swift::Decl*)"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 extension () {
   class let a
 }
diff --git a/validation-test/compiler_crashers_2/4e921915ae337fb5.swift b/validation-test/compiler_crashers_2_fixed/4e921915ae337fb5.swift
similarity index 86%
rename from validation-test/compiler_crashers_2/4e921915ae337fb5.swift
rename to validation-test/compiler_crashers_2_fixed/4e921915ae337fb5.swift
index 72481efdf0a9a..f223e88995d46 100644
--- a/validation-test/compiler_crashers_2/4e921915ae337fb5.swift
+++ b/validation-test/compiler_crashers_2_fixed/4e921915ae337fb5.swift
@@ -1,3 +1,3 @@
 // {"kind":"typecheck","signature":"swift::ConditionalRequirementsRequest::evaluate(swift::Evaluator&, swift::NormalProtocolConformance*) const","signatureAssert":"Assertion failed: (typeSig.getCanonicalSignature().getGenericParams() == extensionSig.getCanonicalSignature().getGenericParams()), function evaluate"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 protocol a typealias b<c> = () extension b : a
diff --git a/validation-test/compiler_crashers_2/548b48b935d4153a.swift b/validation-test/compiler_crashers_2_fixed/548b48b935d4153a.swift
similarity index 86%
rename from validation-test/compiler_crashers_2/548b48b935d4153a.swift
rename to validation-test/compiler_crashers_2_fixed/548b48b935d4153a.swift
index 97ac040706a86..cf72a8ae48cee 100644
--- a/validation-test/compiler_crashers_2/548b48b935d4153a.swift
+++ b/validation-test/compiler_crashers_2_fixed/548b48b935d4153a.swift
@@ -1,4 +1,4 @@
 // {"kind":"typecheck","signature":"swift::NominalType::get(swift::NominalTypeDecl*, swift::Type, swift::ASTContext const&)","signatureAssert":"Assertion failed: ((!Parent || Parent->is<NominalType>() || Parent->is<BoundGenericType>() || Parent->is<UnboundGenericType>()) && \"parent must be a nominal type\"), function get"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 extension() {
   struct a extension a
diff --git a/validation-test/compiler_crashers_2/662d871271047482.swift b/validation-test/compiler_crashers_2_fixed/662d871271047482.swift
similarity index 80%
rename from validation-test/compiler_crashers_2/662d871271047482.swift
rename to validation-test/compiler_crashers_2_fixed/662d871271047482.swift
index d39c4dcb85b60..5c8751cea11dd 100644
--- a/validation-test/compiler_crashers_2/662d871271047482.swift
+++ b/validation-test/compiler_crashers_2_fixed/662d871271047482.swift
@@ -1,5 +1,5 @@
 // {"kind":"typecheck","original":"2e2249a5","signature":"swift::TypeBase::computeCanonicalType()","signatureAssert":"Assertion failed: (Result->isCanonical()), function computeCanonicalType"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 typealias a<b> = (
 >extension a where b ==  {
 c
diff --git a/validation-test/compiler_crashers_2/666bd08556187ed3.swift b/validation-test/compiler_crashers_2_fixed/666bd08556187ed3.swift
similarity index 79%
rename from validation-test/compiler_crashers_2/666bd08556187ed3.swift
rename to validation-test/compiler_crashers_2_fixed/666bd08556187ed3.swift
index 27c4b8479be50..d57b439a466d4 100644
--- a/validation-test/compiler_crashers_2/666bd08556187ed3.swift
+++ b/validation-test/compiler_crashers_2_fixed/666bd08556187ed3.swift
@@ -1,3 +1,3 @@
 // {"kind":"typecheck","signature":"(anonymous namespace)::DeclChecker::visit(swift::Decl*)","signatureAssert":"Assertion failed: (false && \"Huh?\"), function isValidExtendedTypeForTupleExtension"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 extension repeat (
diff --git a/validation-test/compiler_crashers_2_fixed/966aa8f86a7565d3.swift b/validation-test/compiler_crashers_2_fixed/966aa8f86a7565d3.swift
new file mode 100644
index 0000000000000..e14eabc6f6918
--- /dev/null
+++ b/validation-test/compiler_crashers_2_fixed/966aa8f86a7565d3.swift
@@ -0,0 +1,12 @@
+// {"kind":"typecheck","original":"71a26232","signature":"swift::Decl::getDescriptiveKind() const"}
+// RUN: not %target-swift-frontend -typecheck %s
+typealias a = ()
+extension a {
+  func
+    < (b: Self, c: Self)
+  {
+    for (d, e) in repeat (each b    each c) {
+      d < &e
+    }
+  }
+}
diff --git a/validation-test/compiler_crashers_2/983a37d706b4923e.swift b/validation-test/compiler_crashers_2_fixed/983a37d706b4923e.swift
similarity index 80%
rename from validation-test/compiler_crashers_2/983a37d706b4923e.swift
rename to validation-test/compiler_crashers_2_fixed/983a37d706b4923e.swift
index 9299180abfa71..ef84dbe79382f 100644
--- a/validation-test/compiler_crashers_2/983a37d706b4923e.swift
+++ b/validation-test/compiler_crashers_2_fixed/983a37d706b4923e.swift
@@ -1,4 +1,4 @@
 // {"kind":"typecheck","signature":"swift::TypeBase::getNominalParent()","signatureAssert":"Assertion failed: (isa<To>(Val) && \"cast<Ty>() argument of incompatible type!\"), function cast"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 protocol a {
   typealias b<c> = () extension b
diff --git a/validation-test/compiler_crashers_2/9adf18151655a6ae.swift b/validation-test/compiler_crashers_2_fixed/9adf18151655a6ae.swift
similarity index 81%
rename from validation-test/compiler_crashers_2/9adf18151655a6ae.swift
rename to validation-test/compiler_crashers_2_fixed/9adf18151655a6ae.swift
index 37243ebbb1521..1a0b27892b349 100644
--- a/validation-test/compiler_crashers_2/9adf18151655a6ae.swift
+++ b/validation-test/compiler_crashers_2_fixed/9adf18151655a6ae.swift
@@ -1,3 +1,3 @@
 // {"kind":"typecheck","signature":"(anonymous namespace)::DeclChecker::visit(swift::Decl*)","signatureAssert":"Assertion failed: (false && \"Huh?\"), function isValidExtendedTypeForTupleExtension"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 typealias a<b> = (repeat b)protocol c extension a : c
diff --git a/validation-test/compiler_crashers_2/b4746f0a8b4efd96.swift b/validation-test/compiler_crashers_2_fixed/b4746f0a8b4efd96.swift
similarity index 79%
rename from validation-test/compiler_crashers_2/b4746f0a8b4efd96.swift
rename to validation-test/compiler_crashers_2_fixed/b4746f0a8b4efd96.swift
index 84c7ca9db57cb..7b6ebf63339da 100644
--- a/validation-test/compiler_crashers_2/b4746f0a8b4efd96.swift
+++ b/validation-test/compiler_crashers_2_fixed/b4746f0a8b4efd96.swift
@@ -1,3 +1,3 @@
 // {"kind":"typecheck","signature":"(anonymous namespace)::DeclChecker::visit(swift::Decl*)","signatureAssert":"Assertion failed: (false && \"Huh?\"), function isValidExtendedTypeForTupleExtension"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 extension(a[ 0.0 b
diff --git a/validation-test/compiler_crashers_2/d5eedcc26a9c0a1f.swift b/validation-test/compiler_crashers_2_fixed/d5eedcc26a9c0a1f.swift
similarity index 78%
rename from validation-test/compiler_crashers_2/d5eedcc26a9c0a1f.swift
rename to validation-test/compiler_crashers_2_fixed/d5eedcc26a9c0a1f.swift
index 696bbd91d2247..1ad323fd2c252 100644
--- a/validation-test/compiler_crashers_2/d5eedcc26a9c0a1f.swift
+++ b/validation-test/compiler_crashers_2_fixed/d5eedcc26a9c0a1f.swift
@@ -1,5 +1,5 @@
 // {"kind":"typecheck","signature":"swift::TypeBase::getReducedShape()","signatureAssert":"Assertion failed: (!isTypeVariableOrMember()), function getReducedShape"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 typealias a <b> = ()
 extension a {
 c {
diff --git a/validation-test/compiler_crashers_2/e6a483a39992886f.swift b/validation-test/compiler_crashers_2_fixed/e6a483a39992886f.swift
similarity index 81%
rename from validation-test/compiler_crashers_2/e6a483a39992886f.swift
rename to validation-test/compiler_crashers_2_fixed/e6a483a39992886f.swift
index 995c5d5db1242..da06b506ba23a 100644
--- a/validation-test/compiler_crashers_2/e6a483a39992886f.swift
+++ b/validation-test/compiler_crashers_2_fixed/e6a483a39992886f.swift
@@ -1,3 +1,3 @@
 // {"kind":"typecheck","signature":"swift::BuiltinTupleDecl::getTupleSelfType(swift::ExtensionDecl const*) const","signatureAssert":"Assertion failed: (genericParams->getParams().size() == 1), function getTupleSelfType"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 typealias a<b, c> = () extension a
diff --git a/validation-test/compiler_crashers_2/e92d0acb419dec8e.swift b/validation-test/compiler_crashers_2_fixed/e92d0acb419dec8e.swift
similarity index 85%
rename from validation-test/compiler_crashers_2/e92d0acb419dec8e.swift
rename to validation-test/compiler_crashers_2_fixed/e92d0acb419dec8e.swift
index 2eee34e3357e4..561aee26d4f84 100644
--- a/validation-test/compiler_crashers_2/e92d0acb419dec8e.swift
+++ b/validation-test/compiler_crashers_2_fixed/e92d0acb419dec8e.swift
@@ -1,4 +1,4 @@
 // {"kind":"typecheck","signature":"swift::GenericTypeParamType::GenericTypeParamType(swift::GenericTypeParamDecl*, swift::RecursiveTypeProperties)","signatureAssert":"Assertion failed: (param->getDepth() != GenericTypeParamDecl::InvalidDepth), function GenericTypeParamType"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 typealias a = () extension a {
   typealias b<c> = () extension b