diff --git a/nearest-derive/src/emit.rs b/nearest-derive/src/emit.rs
index c15a147..7677c35 100644
--- a/nearest-derive/src/emit.rs
+++ b/nearest-derive/src/emit.rs
@@ -4,7 +4,10 @@ use syn::{Data, DataEnum, DataStruct, DeriveInput, Fields, Variant};
 
 use crate::{
   attrs::{parse_field_attrs, parse_variant_attrs},
-  util::{capitalize, has_flat_bound, opt_where_clause, to_snake_case},
+  util::{
+    capitalize, combine_where, flat_bounded_param_names, has_flat_bound, opt_where_clause,
+    to_snake_case,
+  },
 };
 
 // ---------------------------------------------------------------------------
@@ -176,10 +179,25 @@ fn builder_generics(
 // Structs
 // ---------------------------------------------------------------------------
 
+/// Generate a where clause that adds `Flat` bounds to unbounded type parameters.
+fn outer_where_clause(generics: &syn::Generics) -> TokenStream {
+  let already_bounded = flat_bounded_param_names(generics);
+  let preds: Vec<_> = generics
+    .type_params()
+    .filter(|tp| !already_bounded.contains(&tp.ident.to_string()))
+    .map(|tp| {
+      let ident = &tp.ident;
+      quote! { #ident: ::nearest::Flat }
+    })
+    .collect();
+  combine_where(generics.where_clause.as_ref(), &preds)
+}
+
 fn gen_emit_struct(input: &DeriveInput, data: &DataStruct) -> TokenStream {
   let name = &input.ident;
   let vis = &input.vis;
-  let (impl_generics, ty_generics, input_where) = input.generics.split_for_impl();
+  let (impl_generics, ty_generics, _) = input.generics.split_for_impl();
+  let outer_where = outer_where_clause(&input.generics);
 
   match &data.fields {
     Fields::Named(named) => {
@@ -234,7 +252,7 @@ fn gen_emit_struct(input: &DeriveInput, data: &DataStruct) -> TokenStream {
       };
 
       quote! {
-        impl #impl_generics #name #ty_generics #input_where {
+        impl #impl_generics #name #ty_generics #outer_where {
           #vis fn make #fn_make_generics (#(#fn_params),*) -> impl ::nearest::Emit<Self> {
             struct __Builder #bsg {
               #bpf
@@ -308,7 +326,7 @@ fn gen_emit_struct(input: &DeriveInput, data: &DataStruct) -> TokenStream {
       };
 
       quote! {
-        impl #impl_generics #name #ty_generics #input_where {
+        impl #impl_generics #name #ty_generics #outer_where {
           #vis fn make #fn_make_generics (#(#fn_params),*) -> impl ::nearest::Emit<Self> {
             struct __Builder #bsg {
               #bpf
@@ -340,7 +358,8 @@ fn gen_emit_struct(input: &DeriveInput, data: &DataStruct) -> TokenStream {
 fn gen_emit_enum(input: &DeriveInput, data: &DataEnum) -> TokenStream {
   let name = &input.ident;
   let vis = &input.vis;
-  let (impl_generics, ty_generics, input_where) = input.generics.split_for_impl();
+  let (impl_generics, ty_generics, _) = input.generics.split_for_impl();
+  let outer_where = outer_where_clause(&input.generics);
 
   let methods: Vec<_> = data
     .variants
@@ -350,7 +369,7 @@ fn gen_emit_enum(input: &DeriveInput, data: &DataEnum) -> TokenStream {
     .collect();
 
   quote! {
-    impl #impl_generics #name #ty_generics #input_where {
+    impl #impl_generics #name #ty_generics #outer_where {
       #(#methods)*
     }
   }