diff --git a/misc/cgo/testplugin/src/issue18676/dynamodbstreamsevt/definition.go b/misc/cgo/testplugin/src/issue18676/dynamodbstreamsevt/definition.go
new file mode 100644
index 0000000000..70fd054d08
--- /dev/null
+++ b/misc/cgo/testplugin/src/issue18676/dynamodbstreamsevt/definition.go
@@ -0,0 +1,13 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package dynamodbstreamsevt
+
+import "encoding/json"
+
+var foo json.RawMessage
+
+type Event struct{}
+
+func (e *Event) Dummy() {}
diff --git a/misc/cgo/testplugin/src/issue18676/main.go b/misc/cgo/testplugin/src/issue18676/main.go
new file mode 100644
index 0000000000..c75409dafe
--- /dev/null
+++ b/misc/cgo/testplugin/src/issue18676/main.go
@@ -0,0 +1,31 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// The bug happened like this:
+// 1) The main binary adds an itab for *json.UnsupportedValueError / error
+//    (concrete type / interface type).  This itab goes in hash bucket 0x111.
+// 2) The plugin adds that same itab again.  That makes a cycle in the itab
+//    chain rooted at hash bucket 0x111.
+// 3) The main binary then asks for the itab for *dynamodbstreamsevt.Event /
+//    json.Unmarshaler.  This itab happens to also live in bucket 0x111.
+//    The lookup code goes into an infinite loop searching for this itab.
+// The code is carefully crafted so that the two itabs are both from the
+// same bucket, and so that the second itab doesn't exist in
+// the itab hashmap yet (so the entire linked list must be searched).
+package main
+
+import (
+	"encoding/json"
+	"issue18676/dynamodbstreamsevt"
+	"plugin"
+)
+
+func main() {
+	plugin.Open("plugin.so")
+
+	var x interface{} = (*dynamodbstreamsevt.Event)(nil)
+	if _, ok := x.(json.Unmarshaler); !ok {
+		println("something")
+	}
+}
diff --git a/misc/cgo/testplugin/src/issue18676/plugin.go b/misc/cgo/testplugin/src/issue18676/plugin.go
new file mode 100644
index 0000000000..8a3b85a75c
--- /dev/null
+++ b/misc/cgo/testplugin/src/issue18676/plugin.go
@@ -0,0 +1,11 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "C"
+
+import "issue18676/dynamodbstreamsevt"
+
+func F(evt *dynamodbstreamsevt.Event) {}
diff --git a/misc/cgo/testplugin/test.bash b/misc/cgo/testplugin/test.bash
index 584b83c744..ab7430acc3 100755
--- a/misc/cgo/testplugin/test.bash
+++ b/misc/cgo/testplugin/test.bash
@@ -16,7 +16,7 @@ goarch=$(go env GOARCH)
 
 function cleanup() {
 	rm -f plugin*.so unnamed*.so iface*.so
-	rm -rf host pkg sub iface
+	rm -rf host pkg sub iface issue18676
 }
 trap cleanup EXIT
 
@@ -38,3 +38,9 @@ GOPATH=$(pwd) go build -buildmode=plugin iface_a
 GOPATH=$(pwd) go build -buildmode=plugin iface_b
 GOPATH=$(pwd) go build iface
 LD_LIBRARY_PATH=$(pwd) ./iface
+
+# Test for issue 18676 - make sure we don't add the same itab twice.
+# The buggy code hangs forever, so use a timeout to check for that.
+GOPATH=$(pwd) go build -buildmode=plugin -o plugin.so src/issue18676/plugin.go
+GOPATH=$(pwd) go build -o issue18676 src/issue18676/main.go
+timeout 10s ./issue18676
diff --git a/src/runtime/plugin.go b/src/runtime/plugin.go
index 80869e1b1c..8edb29c9fe 100644
--- a/src/runtime/plugin.go
+++ b/src/runtime/plugin.go
@@ -56,7 +56,9 @@ func plugin_lastmoduleinit() (path string, syms map[string]interface{}, mismatch
 
 	lock(&ifaceLock)
 	for _, i := range md.itablinks {
-		additab(i, true, false)
+		if i.inhash == 0 {
+			additab(i, true, false)
+		}
 	}
 	unlock(&ifaceLock)