diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index f23b635aec9f70a3a9c7eafa89875beca58fb7ba..12139e1d86279ca25f6e9e001b752fc705de7021 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -17387,9 +17387,15 @@ build_enumerator (tree name, tree value, tree enumtype, tree attributes,
   tree type;
 
   /* scalar_constant_value will pull out this expression, so make sure
-     it's folded as appropriate.  */
+     it's folded as appropriate.
+
+     Creating a TARGET_EXPR in a template breaks when substituting, and
+     here we would create it for instance when using a class prvalue with
+     a user-defined conversion function.  So don't use such a tree.  We
+     instantiate VALUE here to get errors about bad enumerators even in
+     a template that does not get instantiated.  */
   if (processing_template_decl)
-    value = fold_non_dependent_expr (value);
+    value = maybe_fold_non_dependent_expr (value);
 
   /* If the VALUE was erroneous, pretend it wasn't there; that will
      result in the enum being assigned the next value in sequence.  */
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-recursion2.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-recursion2.C
new file mode 100644
index 0000000000000000000000000000000000000000..f268f52e2b5bd8015e31c3c0e7f1d21e67000b77
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-recursion2.C
@@ -0,0 +1,22 @@
+// PR c++/115657
+// { dg-do compile { target c++14 } }
+// { dg-options "-Wall" }
+
+// Like constexpr-recursion1.C but use a class with a conversion function.
+
+struct X {
+  constexpr operator int() { return 0; }
+};
+
+template <int N>
+constexpr X f1 ()
+{
+  enum E { a = f1<0> () }; // { dg-error "called in a constant expression before its definition is complete|is not an integer constant" }
+  return {};
+}
+
+constexpr X f3 ()
+{
+  enum E { a = f3 () };	// { dg-error "called in a constant expression before its definition is complete|is not an integer constant" }
+  return {};
+}
diff --git a/gcc/testsuite/g++.dg/template/conv21.C b/gcc/testsuite/g++.dg/template/conv21.C
new file mode 100644
index 0000000000000000000000000000000000000000..1dc7b3d50d9e50fef0bfdb62f227d297ad35d86b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/conv21.C
@@ -0,0 +1,14 @@
+// PR c++/115657
+// { dg-do compile { target c++11 } }
+
+struct NonIntegral
+{
+    constexpr operator int() { return 0; }
+};
+
+template<typename T> struct TemplatedStructural
+{
+    enum { e = NonIntegral{} };
+};
+
+template struct TemplatedStructural<void>;