diff --git a/include/clang/Basic/DiagnosticGroups.td b/include/clang/Basic/DiagnosticGroups.td
index a7ef218..7e0438a 100644
--- a/include/clang/Basic/DiagnosticGroups.td
+++ b/include/clang/Basic/DiagnosticGroups.td
@@ -254,7 +254,6 @@
 def : DiagGroup<"strict-overflow">;
 
 def InvalidOffsetof : DiagGroup<"invalid-offsetof">;
-def LambdaExtensions : DiagGroup<"lambda-extensions">;
 def : DiagGroup<"strict-prototypes">;
 def StrictSelector : DiagGroup<"strict-selector-match">;
 def MethodDuplicate : DiagGroup<"duplicate-method-match">;
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 1330ad6..e6e67b4 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -4789,9 +4789,6 @@
     "incomplete result type %0 in lambda expression">;
   def err_lambda_objc_object_result : Error<
     "non-pointer Objective-C class type %0 in lambda expression result">;
-  def ext_lambda_default_arguments : ExtWarn<
-    "C++11 forbids default arguments for lambda expressions">,
-    InGroup<LambdaExtensions>;
   def err_noreturn_lambda_has_return_expr : Error<
     "lambda declared 'noreturn' should not return">;
   def warn_maybe_falloff_nonvoid_lambda : Warning<
diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index a318f64..d2051b5 100644
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -636,22 +636,12 @@
   bool IsLambda = FD->getOverloadedOperator() == OO_Call &&
                   isa<CXXMethodDecl>(FD) &&
                   cast<CXXMethodDecl>(FD)->getParent()->isLambda();
-              
+
   // Find first parameter with a default argument
   for (p = 0; p < NumParams; ++p) {
     ParmVarDecl *Param = FD->getParamDecl(p);
-    if (Param->hasDefaultArg()) {
-      // C++11 [expr.prim.lambda]p5:
-      //   [...] Default arguments (8.3.6) shall not be specified in the 
-      //   parameter-declaration-clause of a lambda-declarator.
-      //
-      // FIXME: Core issue 974 strikes this sentence, we only provide an
-      // extension warning.
-      if (IsLambda)
-        Diag(Param->getLocation(), diag::ext_lambda_default_arguments)
-          << Param->getDefaultArgRange();
+    if (Param->hasDefaultArg())
       break;
-    }
   }
 
   // C++ [dcl.fct.default]p4:
diff --git a/test/CXX/expr/expr.prim/expr.prim.lambda/default-arguments.cpp b/test/CXX/expr/expr.prim/expr.prim.lambda/default-arguments.cpp
index 5dac886..38d5d0a 100644
--- a/test/CXX/expr/expr.prim/expr.prim.lambda/default-arguments.cpp
+++ b/test/CXX/expr/expr.prim/expr.prim.lambda/default-arguments.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -std=c++11 %s -Wno-lambda-extensions -verify
+// RUN: %clang_cc1 -fsyntax-only -std=c++11 %s -verify
 
 void defargs() {
   auto l1 = [](int i, int j = 17, int k = 18) { return i + j + k; };
diff --git a/test/CXX/expr/expr.prim/expr.prim.lambda/p5.cpp b/test/CXX/expr/expr.prim/expr.prim.lambda/p5.cpp
index 9dffc1f..dc2c209 100644
--- a/test/CXX/expr/expr.prim/expr.prim.lambda/p5.cpp
+++ b/test/CXX/expr/expr.prim/expr.prim.lambda/p5.cpp
@@ -39,12 +39,10 @@
   bogus_override_if_virtual<decltype(l)> bogus;
 }
 
-// Default arguments (8.3.6) shall not be specified in the
-// parameter-declaration-clause of a lambda- declarator.
-// Note: Removed by core issue 974.
+// Core issue 974: default arguments (8.3.6) may be specified in the
+// parameter-declaration-clause of a lambda-declarator.
 int test_default_args() {
-  return [](int i = 5,  // expected-warning{{C++11 forbids default arguments for lambda expressions}}
-            int j = 17) { return i+j;}(5, 6);
+  return [](int i = 5, int j = 17) { return i+j;}(5, 6);
 }
 
 // Any exception-specification specified on a lambda-expression