Index: lib/Sema/SemaExpr.cpp
===================================================================
--- lib/Sema/SemaExpr.cpp
+++ lib/Sema/SemaExpr.cpp
@@ -13005,7 +13005,7 @@
       if (MethodDecl->isDefaulted() && !MethodDecl->isDeleted()) {
         if (MethodDecl->isCopyAssignmentOperator())
           DefineImplicitCopyAssignment(Loc, MethodDecl);
-        else
+        else if (MethodDecl->isMoveAssignmentOperator())
           DefineImplicitMoveAssignment(Loc, MethodDecl);
       }
     } else if (isa<CXXConversionDecl>(MethodDecl) &&
Index: test/SemaCXX/cxx0x-defaulted-functions.cpp
===================================================================
--- test/SemaCXX/cxx0x-defaulted-functions.cpp
+++ test/SemaCXX/cxx0x-defaulted-functions.cpp
@@ -196,3 +196,15 @@
   A<int> a;
   B<int> b; // expected-note {{here}}
 }
+
+namespace PR27941 {
+struct ExplicitBool {
+  ExplicitBool &operator=(bool) = default; // expected-error{{only special member functions may be defaulted}}
+  int member;
+};
+
+int fn() {
+  ExplicitBool t;
+  t = true;
+}
+}