diff --git a/arm/armspec/spec.go b/arm/armspec/spec.go
index f76fab0..e02d092 100644
--- a/arm/armspec/spec.go
+++ b/arm/armspec/spec.go
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !386 go1.8
+// ... see golang.org/issue/12840
+
 // Armspec reads the ``ARM Architecture Reference Manual''
 // to collect instruction encoding details and writes those details to standard output
 // in JSON format.
diff --git a/vendor/rsc.io/pdf/lex.go b/vendor/rsc.io/pdf/lex.go
index ee73fd9..85bfdcc 100644
--- a/vendor/rsc.io/pdf/lex.go
+++ b/vendor/rsc.io/pdf/lex.go
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !386 go1.8
+// ... see golang.org/issue/12840
+
 // Reading of PDF tokens and objects from a raw byte stream.
 
 package pdf
diff --git a/vendor/rsc.io/pdf/page.go b/vendor/rsc.io/pdf/page.go
index 9c7d688..6669907 100644
--- a/vendor/rsc.io/pdf/page.go
+++ b/vendor/rsc.io/pdf/page.go
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !386 go1.8
+// ... see golang.org/issue/12840
+
 package pdf
 
 import (
diff --git a/vendor/rsc.io/pdf/ps.go b/vendor/rsc.io/pdf/ps.go
index 90c551e..69292aa 100644
--- a/vendor/rsc.io/pdf/ps.go
+++ b/vendor/rsc.io/pdf/ps.go
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !386 go1.8
+// ... see golang.org/issue/12840
+
 package pdf
 
 import (
diff --git a/vendor/rsc.io/pdf/read.go b/vendor/rsc.io/pdf/read.go
index da6c2c6..84cb17a 100644
--- a/vendor/rsc.io/pdf/read.go
+++ b/vendor/rsc.io/pdf/read.go
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !386 go1.8
+// ... see golang.org/issue/12840
+
 // Package pdf implements reading of PDF files.
 //
 // Overview