diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 56cccf2a67b..848c2fda203 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -514,6 +514,10 @@ Wcast-qual
 C ObjC C++ ObjC++ Var(warn_cast_qual) Warning
 Warn about casts which discard qualifiers.
 
+Wcast-user-defined
+C++ ObjC++ Var(warn_cast_user_defined) Warning Init(1)
+Warn about a cast to reference type that does not use a related user-defined conversion function.
+
 Wcatch-value
 C++ ObjC++ Warning Alias(Wcatch-value=, 1, 0)
 Warn about catch handlers of non-reference type.
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 15b5647298e..dbdd7c29fe8 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -2034,7 +2034,17 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags,
 	 recalculate the second conversion sequence.  */
       for (conversion *t = conv; t; t = next_conversion (t))
 	if (t->kind == ck_user
-	    && DECL_CONV_FN_P (t->cand->fn))
+	    && c_cast_p && !maybe_valid_p)
+	  {
+	    if (complain & tf_warning)
+	      warning (OPT_Wcast_user_defined,
+		       "casting %qT to %qT does not use %qD",
+		       from, rto, t->cand->fn);
+	    /* Don't let recalculation try to make this valid.  */
+	    break;
+	  }
+	else if (t->kind == ck_user
+		 && DECL_CONV_FN_P (t->cand->fn))
 	  {
 	    tree ftype = TREE_TYPE (TREE_TYPE (t->cand->fn));
 	    /* A prvalue of non-class type is cv-unqualified.  */
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 5d5e70c3033..e3285587e4e 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -9391,6 +9391,19 @@ In a cast involving pointer to member types this warning warns whenever
 the type cast is changing the pointer to member type.
 This warning is enabled by @option{-Wextra}.
 
+@opindex Wcast-user-defined
+@opindex Wno-cast-user-defined
+@item -Wcast-user-defined
+Warn when a cast to reference type does not involve a user-defined
+conversion that the programmer might expect to be called.
+
+@smallexample
+struct A @{ operator const int&(); @} a;
+auto r = (int&)a; // warning
+@end smallexample
+
+This warning is enabled by default.
+
 @opindex Wwrite-strings
 @opindex Wno-write-strings
 @item -Wwrite-strings
diff --git a/gcc/testsuite/g++.dg/conversion/ref12.C b/gcc/testsuite/g++.dg/conversion/ref12.C
new file mode 100644
index 00000000000..27ed9122769
--- /dev/null
+++ b/gcc/testsuite/g++.dg/conversion/ref12.C
@@ -0,0 +1,20 @@
+// PR c++/113141
+
+struct Matrix { };
+
+struct TPoint3 { private: operator const Matrix(); };
+
+void f(Matrix&);
+
+int main() {
+  TPoint3 X;
+  Matrix& m = (Matrix &)X;	// { dg-warning "does not use" }
+  f((Matrix &)X);		// { dg-warning "does not use" }
+}
+
+struct A { private: operator const int&(); } a;
+int &r = (int&)a;		// { dg-warning "does not use" }
+
+struct B { B(int); };
+int i;
+B &br = (B&)i;			// { dg-warning "does not use" }