Index: cp/decl.c
===================================================================
--- cp/decl.c	(revision 197572)
+++ cp/decl.c	(working copy)
@@ -1203,6 +1203,14 @@ validate_constexpr_redeclaration (tree old_decl, t
 	= DECL_DECLARED_CONSTEXPR_P (new_decl);
       return true;
     }
+  /* 7.1.5 [dcl.constexpr]
+     Note: An explicit specialization can differ from the template
+     declaration with respect to the constexpr specifier.  */
+  if (TREE_CODE (old_decl) == FUNCTION_DECL
+      && TREE_CODE (new_decl) == FUNCTION_DECL
+      && ! DECL_TEMPLATE_SPECIALIZATION (old_decl)
+      && DECL_TEMPLATE_SPECIALIZATION (new_decl))
+    return true;
   error ("redeclaration %qD differs in %<constexpr%>", new_decl);
   error ("from previous declaration %q+D", old_decl);
   return false;
Index: testsuite/g++.dg/cpp0x/constexpr-specialization.C
===================================================================
--- testsuite/g++.dg/cpp0x/constexpr-specialization.C	(revision 0)
+++ testsuite/g++.dg/cpp0x/constexpr-specialization.C	(working copy)
@@ -0,0 +1,12 @@
+// PR c++/56871
+// { dg-options "-std=c++11" }
+
+template<typename T> constexpr int foo(T);
+template<> int foo(int);
+template<> int foo(int);            // { dg-error "previous" }
+template<> constexpr int foo(int);  // { dg-error "redeclaration" }
+
+template<typename T> int bar(T);
+template<> constexpr int bar(int);
+template<> constexpr int bar(int);  // { dg-error "previous" }
+template<> int bar(int);            // { dg-error "redeclaration" }