diff --git a/BinaryEncoding.md b/BinaryEncoding.md
index 5c59b351..8035b27c 100644
--- a/BinaryEncoding.md
+++ b/BinaryEncoding.md
@@ -195,8 +195,8 @@ part of the payload.
 | ----- |  ----- | ----- |
 | id | `varuint7` | section code |
 | payload_len  | `varuint32` | size of this section in bytes |
-| name_len | `varuint32` ? | length of the section name in bytes, present if `id == 0` |
-| name | `bytes` ? | section name string, present if `id == 0` |
+| name_len | `varuint32` ? | length of `name` in bytes, present if `id == 0` |
+| name | `bytes` ? | section name: valid UTF-8 byte sequence, present if `id == 0` |
 | payload_data  | `bytes` | content of this section, of length `payload_len - sizeof(name) - sizeof(name_len)` |
 
 Each known section is optional and may appear at most once. Custom sections all have the same `id` (0), and can be named non-uniquely (all bytes composing their names may be identical).
@@ -252,10 +252,10 @@ The import section declares all imports that will be used in the module.
 
 | Field | Type | Description |
 | ----- | ---- | ----------- |
-| module_len | `varuint32` | module string length |
-| module_str | `bytes` | module string of `module_len` bytes |
-| field_len | `varuint32` | field name length |
-| field_str | `bytes` | field name string of `field_len` bytes |
+| module_len | `varuint32` | length of `module_str` in bytes |
+| module_str | `bytes` | module name: valid UTF-8 byte sequence |
+| field_len | `varuint32` | length of `field_str` in bytes |
+| field_str | `bytes` | field name: valid UTF-8 byte sequence |
 | kind | `external_kind` | the kind of definition being imported |
 
 Followed by, if the `kind` is `Function`:
@@ -355,8 +355,8 @@ The encoding of the [Export section](Modules.md#exports):
 
 | Field | Type | Description |
 | ----- | ---- | ----------- |
-| field_len | `varuint32` | field name string length |
-| field_str | `bytes` | field name string of `field_len` bytes |
+| field_len | `varuint32` | length of `field_str` in bytes |
+| field_str | `bytes` | field name: valid UTF-8 byte sequence |
 | kind | `external_kind` | the kind of definition being exported |
 | index | `varuint32` | the index into the corresponding [index space](Modules.md) |
 
@@ -470,8 +470,8 @@ where a `naming` is encoded as:
 | Field | Type | Description |
 | ----- | ---- | ----------- |
 | index | `varuint32` | the index which is being named |
-| name_len | `varuint32` | number of bytes in name_str |
-| name_str | `bytes` | binary encoding of the name |
+| name_len | `varuint32` | length of `name_str` in bytes |
+| name_str | `bytes` | UTF-8 encoding of the name |
 
 #### Function names
 
diff --git a/Modules.md b/Modules.md
index 708b79ef..37a9dfd9 100644
--- a/Modules.md
+++ b/Modules.md
@@ -48,7 +48,8 @@ In the future, other kinds of imports may be added. Imports are designed to
 allow modules to share code and data while still allowing separate compilation
 and caching.
 
-All imports include two opaque names: a *module name* and an *export name*. The
+All imports include two opaque names: a *module name* and an *export name*,
+which are required to be [valid UTF-8]. The
 interpretation of these names is up to the host environment but designed to
 allow a host environments, like the [Web](Web.md), to support a two-level
 namespace.
@@ -108,7 +109,8 @@ native `syscall`. For example, a shell environment could define a builtin
 
 A module can declare a sequence of **exports** which are returned at
 instantiation time to the host environment. Each export has three fields:
-a *name*, whose meaning is defined by the host environment, a *type*,
+a *name*, which is required to be [valid UTF-8],
+whose meaning is defined by the host environment, a *type*,
 indicating whether the export is a function, global, memory or table, and
 an *index* into the type's corresponding [index space](Modules.md).
 
@@ -380,3 +382,4 @@ In the future, operators like `i32.add` could be added to allow more expressive
 [future types]: FutureFeatures.md#more-table-operators-and-types
 [future dom]: FutureFeatures.md#gc/dom-integration
 [future multiple tables]: FutureFeatures.md#multiple-tables-and-memories
+[valid UTF-8]: https://encoding.spec.whatwg.org/#utf-8-decode-without-bom-or-fail