diff --git a/dawn.json b/dawn.json
index 79e5f4e23c..4151b95368 100644
--- a/dawn.json
+++ b/dawn.json
@@ -572,7 +572,7 @@
                     {"name": "group index", "type": "uint32_t"},
                     {"name": "group", "type": "bind group"},
                     {"name": "dynamic offset count", "type": "uint32_t", "default": "0"},
-                    {"name": "dynamic offsets", "type": "uint32_t", "annotation": "const*", "length": "dynamic offset count", "optional": true}
+                    {"name": "dynamic offsets", "type": "uint32_t", "annotation": "const*", "length": "dynamic offset count", "default": "nullptr"}
                 ]
             },
             {
@@ -1229,7 +1229,7 @@
                     {"name": "group index", "type": "uint32_t"},
                     {"name": "group", "type": "bind group"},
                     {"name": "dynamic offset count", "type": "uint32_t", "default": "0"},
-                    {"name": "dynamic offsets", "type": "uint32_t", "annotation": "const*", "length": "dynamic offset count", "optional": true}
+                    {"name": "dynamic offsets", "type": "uint32_t", "annotation": "const*", "length": "dynamic offset count", "default": "nullptr"}
                 ]
             },
             {
@@ -1393,7 +1393,7 @@
                     {"name": "group index", "type": "uint32_t"},
                     {"name": "group", "type": "bind group"},
                     {"name": "dynamic offset count", "type": "uint32_t", "default": "0"},
-                    {"name": "dynamic offsets", "type": "uint32_t", "annotation": "const*", "length": "dynamic offset count", "optional": true}
+                    {"name": "dynamic offsets", "type": "uint32_t", "annotation": "const*", "length": "dynamic offset count", "default": "nullptr"}
                 ]
             },
             {
diff --git a/generator/templates/dawn_wire/WireCmd.cpp b/generator/templates/dawn_wire/WireCmd.cpp
index 4816ee122c..2c372905b0 100644
--- a/generator/templates/dawn_wire/WireCmd.cpp
+++ b/generator/templates/dawn_wire/WireCmd.cpp
@@ -361,6 +361,10 @@ namespace {
             {% set memberName = as_varName(member.name) %}
 
             {% if member.type.category != "object" and member.optional %}
+                //* Non-constant length optional members use length=0 to denote they aren't present.
+                //* Otherwise we could have length=N and has_member=false, causing reads from an
+                //* uninitialized pointer.
+                {{ assert(member.length == "constant") }}
                 bool has_{{memberName}} = transfer->has_{{memberName}};
                 record->{{memberName}} = nullptr;
                 if (has_{{memberName}})