Index: c-family/c.opt
===================================================================
--- c-family/c.opt	(revision 202384)
+++ c-family/c.opt	(working copy)
@@ -339,6 +339,10 @@ Wdeclaration-after-statement
 C ObjC Var(warn_declaration_after_statement) Warning
 Warn when a declaration is found after a statement
 
+Wdelete-incomplete
+C++ ObjC++ Var(warn_delete_incomplete) Init(1) Warning
+Warn when deleting a pointer to incomplete type
+
 Wdelete-non-virtual-dtor
 C++ ObjC++ Var(warn_delnonvdtor) Warning LangEnabledBy(C++ ObjC++,Wall)
 Warn about deleting polymorphic objects with non-virtual destructors
Index: cp/init.c
===================================================================
--- cp/init.c	(revision 202384)
+++ cp/init.c	(working copy)
@@ -3078,7 +3078,7 @@ build_vec_delete_1 (tree base, tree maxindex, tree
 {
   tree virtual_size;
   tree ptype = build_pointer_type (type = complete_type (type));
-  tree size_exp = size_in_bytes (type);
+  tree size_exp;
 
   /* Temporary variables used by the loop.  */
   tree tbase, tbase_init;
@@ -3106,6 +3106,23 @@ build_vec_delete_1 (tree base, tree maxindex, tree
   if (base == error_mark_node || maxindex == error_mark_node)
     return error_mark_node;
 
+  if (!COMPLETE_TYPE_P (type))
+    {
+      if ((complain & tf_warning)
+	  && warning (OPT_Wdelete_incomplete,
+		      "possible problem detected in invocation of "
+		      "delete [] operator:"))
+       {
+         cxx_incomplete_type_diagnostic (base, type, DK_WARNING);
+         inform (input_location, "neither the destructor nor the "
+                 "class-specific operator delete [] will be called, "
+                 "even if they are declared when the class is defined");
+       }
+      return build_builtin_delete_call (base);
+    } 
+
+  size_exp = size_in_bytes (type);
+
   if (! MAYBE_CLASS_TYPE_P (type) || TYPE_HAS_TRIVIAL_DESTRUCTOR (type))
     goto no_destructor;
 
@@ -3820,11 +3837,13 @@ build_delete (tree type, tree addr, special_functi
 	  if (!COMPLETE_TYPE_P (type))
 	    {
 	      if ((complain & tf_warning)
-		  && warning (0, "possible problem detected in invocation of "
+		  && warning (OPT_Wdelete_incomplete,
+			      "possible problem detected in invocation of "
 			      "delete operator:"))
 		{
 		  cxx_incomplete_type_diagnostic (addr, type, DK_WARNING);
-		  inform (input_location, "neither the destructor nor the class-specific "
+		  inform (input_location,
+			  "neither the destructor nor the class-specific "
 			  "operator delete will be called, even if they are "
 			  "declared when the class is defined");
 		}
Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi	(revision 202384)
+++ doc/invoke.texi	(working copy)
@@ -240,8 +240,8 @@ Objective-C and Objective-C++ Dialects}.
 -Wno-attributes -Wno-builtin-macro-redefined @gol
 -Wc++-compat -Wc++11-compat -Wcast-align  -Wcast-qual  @gol
 -Wchar-subscripts -Wclobbered  -Wcomment -Wconditionally-supported  @gol
--Wconversion  -Wcoverage-mismatch  -Wno-cpp  -Wno-deprecated  @gol
--Wno-deprecated-declarations -Wdisabled-optimization  @gol
+-Wconversion -Wcoverage-mismatch  -Wdelete-incomplete -Wno-cpp  @gol
+-Wno-deprecated -Wno-deprecated-declarations -Wdisabled-optimization  @gol
 -Wno-div-by-zero -Wdouble-promotion -Wempty-body  -Wenum-compare @gol
 -Wno-endif-labels -Werror  -Werror=* @gol
 -Wfatal-errors  -Wfloat-equal  -Wformat  -Wformat=2 @gol
@@ -4490,6 +4490,12 @@ types. @option{-Wconversion-null} is enabled by de
 Warn when a literal '0' is used as null pointer constant.  This can
 be useful to facilitate the conversion to @code{nullptr} in C++11.
 
+@item -Wdelete-incomplete @r{(C++ and Objective-C++ only)}
+@opindex Wdelete-incomplete
+@opindex Wno-delete-incomplete
+Warn when deleting a pointer to incomplete type, which may cause
+undefined behavior at runtime.  This warning is enabled by default.
+
 @item -Wuseless-cast @r{(C++ and Objective-C++ only)}
 @opindex Wuseless-cast
 @opindex Wno-useless-cast
Index: testsuite/g++.dg/init/delete1.C
===================================================================
--- testsuite/g++.dg/init/delete1.C	(revision 202384)
+++ testsuite/g++.dg/init/delete1.C	(working copy)
@@ -1,7 +1,7 @@
 // PR c++/19811
 
-class C; // { dg-error "forward" }
+class C; // { dg-warning "forward" }
 
 void foo(void *p) {
-  delete [] ((C*)p) ; // { dg-error "" }
+  delete [] ((C*)p) ; // { dg-warning "problem|incomplete" }
 }
Index: testsuite/g++.dg/warn/Wdelete-incomplete-1.C
===================================================================
--- testsuite/g++.dg/warn/Wdelete-incomplete-1.C	(revision 0)
+++ testsuite/g++.dg/warn/Wdelete-incomplete-1.C	(working copy)
@@ -0,0 +1,7 @@
+// PR c++/43452
+
+class Foo;         // { dg-warning "forward" }
+int main() {
+   Foo* p;         // { dg-warning "incomplete" }
+   delete [] p;    // { dg-warning "problem" }
+}
Index: testsuite/g++.dg/warn/Wdelete-incomplete-2.C
===================================================================
--- testsuite/g++.dg/warn/Wdelete-incomplete-2.C	(revision 0)
+++ testsuite/g++.dg/warn/Wdelete-incomplete-2.C	(working copy)
@@ -0,0 +1,8 @@
+// PR c++/43452
+// { dg-options -Wno-delete-incomplete }
+
+class Foo;
+int main() {
+   Foo* p;
+   delete [] p;
+}