diff --git a/components/script/dom/bindings/codegen/CodegenRust.py b/components/script/dom/bindings/codegen/CodegenRust.py
index f6bb21932e6..36dc8a3c380 100644
--- a/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/components/script/dom/bindings/codegen/CodegenRust.py
@@ -88,6 +88,11 @@ def stripTrailingWhitespace(text):
     return '\n'.join(lines) + tail
 
 
+def innerSequenceType(type):
+    assert type.isSequence()
+    return type.inner.inner if type.nullable() else type.inner
+
+
 def MakeNativeName(name):
     return name[0].upper() + name[1:]
 
@@ -714,7 +719,7 @@ def getJSToNativeConversionInfo(type, descriptorProvider, failureCode=None,
         raise TypeError("Can't handle array arguments yet")
 
     if type.isSequence():
-        innerInfo = getJSToNativeConversionInfo(type.unroll(), descriptorProvider)
+        innerInfo = getJSToNativeConversionInfo(innerSequenceType(type), descriptorProvider)
         declType = CGWrapper(innerInfo.declType, pre="Vec<", post=">")
         config = getConversionConfigForType(type, isEnforceRange, isClamp, treatNullAs)
 
@@ -1303,8 +1308,7 @@ def getRetvalDeclarationForType(returnType, descriptorProvider):
     if returnType.isObject() or returnType.isSpiderMonkeyInterface():
         return CGGeneric("*mut JSObject")
     if returnType.isSequence():
-        inner = returnType.unroll()
-        result = getRetvalDeclarationForType(inner, descriptorProvider)
+        result = getRetvalDeclarationForType(innerSequenceType(returnType), descriptorProvider)
         result = CGWrapper(result, pre="Vec<", post=">")
         if returnType.nullable():
             result = CGWrapper(result, pre="Option<", post=">")
@@ -3744,7 +3748,7 @@ def getUnionTypeTemplateVars(type, descriptorProvider):
         typeName = name
     elif type.isSequence():
         name = type.name
-        inner = getUnionTypeTemplateVars(type.unroll(), descriptorProvider)
+        inner = getUnionTypeTemplateVars(innerSequenceType(type), descriptorProvider)
         typeName = "Vec<" + inner["typeName"] + ">"
     elif type.isArray():
         name = str(type)
diff --git a/components/script/dom/testbinding.rs b/components/script/dom/testbinding.rs
index 8ee6dfe8025..c117c6a31aa 100644
--- a/components/script/dom/testbinding.rs
+++ b/components/script/dom/testbinding.rs
@@ -9,7 +9,7 @@ use dom::bindings::codegen::Bindings::FunctionBinding::Function;
 use dom::bindings::codegen::Bindings::TestBindingBinding;
 use dom::bindings::codegen::Bindings::TestBindingBinding::{TestBindingMethods, TestDictionary};
 use dom::bindings::codegen::Bindings::TestBindingBinding::{TestDictionaryDefaults, TestEnum};
-use dom::bindings::codegen::UnionTypes::{BlobOrBoolean, BlobOrBlobSequence};
+use dom::bindings::codegen::UnionTypes::{BlobOrBoolean, BlobOrBlobSequence, LongOrLongSequenceSequence};
 use dom::bindings::codegen::UnionTypes::{BlobOrString, BlobOrUnsignedLong, EventOrString};
 use dom::bindings::codegen::UnionTypes::{EventOrUSVString, HTMLElementOrLong};
 use dom::bindings::codegen::UnionTypes::{HTMLElementOrUnsignedLongOrStringOrBoolean, LongSequenceOrBoolean};
@@ -572,6 +572,17 @@ impl TestBindingMethods for TestBinding {
     fn FuncControlledMethodDisabled(&self) {}
     fn FuncControlledMethodEnabled(&self) {}
 
+    fn PassSequenceSequence(&self, _seq: Vec<Vec<i32>>) {}
+    fn ReturnSequenceSequence(&self) -> Vec<Vec<i32>> { vec![] }
+    fn PassUnionSequenceSequence(&self, seq: LongOrLongSequenceSequence) {
+        match seq {
+            LongOrLongSequenceSequence::Long(_) => (),
+            LongOrLongSequenceSequence::LongSequenceSequence(seq) => {
+                let _seq: Vec<Vec<i32>> = seq;
+            }
+        }
+    }
+
     #[allow(unsafe_code)]
     fn CrashHard(&self) {
         static READ_ONLY_VALUE: i32 = 0;
diff --git a/components/script/dom/webidls/TestBinding.webidl b/components/script/dom/webidls/TestBinding.webidl
index 48e647ee7bc..50240b9793d 100644
--- a/components/script/dom/webidls/TestBinding.webidl
+++ b/components/script/dom/webidls/TestBinding.webidl
@@ -409,6 +409,10 @@ interface TestBinding {
   void passVariadicAny(any... args);
   void passVariadicObject(object... args);
 
+  void passSequenceSequence(sequence<sequence<long>> seq);
+  sequence<sequence<long>> returnSequenceSequence();
+  void passUnionSequenceSequence((long or sequence<sequence<long>>) seq);
+
   static attribute boolean booleanAttributeStatic;
   static void receiveVoidStatic();
   boolean BooleanMozPreference(DOMString pref_name);