diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index d6e1b8b15b0..547edadab3d 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,9 @@
+2016-12-12  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/78647
+	* c-common.c (attribute_fallthrough_p): Return false for
+	error_mark_node.
+
 2016-12-08  Martin Sebor  <msebor@redhat.com>
 
 	PR c/78284
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 0749361fb44..c8e1f0da3c1 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -5558,6 +5558,8 @@ parse_optimize_options (tree args, bool attr_p)
 bool
 attribute_fallthrough_p (tree attr)
 {
+  if (attr == error_mark_node)
+   return false;
   tree t = lookup_attribute ("fallthrough", attr);
   if (t == NULL_TREE)
     return false;
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index f1f518411db..d6657b574d9 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2016-12-12  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/78647
+	* g++.dg/parse/error58.C: New.
+
 2016-12-12  David Malcolm  <dmalcolm@redhat.com>
 
 	PR preprocessor/78680
diff --git a/gcc/testsuite/g++.dg/parse/error58.C b/gcc/testsuite/g++.dg/parse/error58.C
new file mode 100644
index 00000000000..5ed6e1e19bd
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/error58.C
@@ -0,0 +1,7 @@
+// PR c++/78647
+// { dg-do compile { target c++11 } }
+// { dg-options "-w" }
+
+struct A;
+void foo ();
+void f() { alignas (foo (A)); } // { dg-error "expected" "" }