diff --git a/cranelift/isle/src/codegen.rs b/cranelift/isle/src/codegen.rs
index e080f30a25..4a12c5d7c9 100644
--- a/cranelift/isle/src/codegen.rs
+++ b/cranelift/isle/src/codegen.rs
@@ -2,8 +2,9 @@
 
 use crate::error::Error;
 use crate::ir::{lower_rule, ExprSequence, PatternInst, PatternSequence};
-use crate::sema::{RuleId, TermEnv, TermId, TypeEnv};
+use crate::sema::{RuleId, TermEnv, TermId, Type, TypeEnv};
 use std::collections::HashMap;
+use std::fmt::Write;
 
 /// One "input symbol" for the decision tree that handles matching on
 /// a term. Each symbol represents one step: we either run a match op,
@@ -509,9 +510,49 @@ impl<'a> Codegen<'a> {
     }
 
     pub fn generate_rust(&self) -> Result<String, Error> {
-        use std::fmt::Write;
         let mut code = String::new();
         writeln!(&mut code, "// GENERATED BY ISLE. DO NOT EDIT!")?;
+        writeln!(
+            &mut code,
+            "use super::*;  // Pulls in all external types and ctors/etors"
+        )?;
+        self.generate_internal_types(&mut code)?;
         Ok(code)
     }
+
+    fn generate_internal_types(&self, code: &mut dyn Write) -> Result<(), Error> {
+        for ty in &self.typeenv.types {
+            match ty {
+                &Type::Enum {
+                    name,
+                    is_extern,
+                    ref variants,
+                    pos,
+                    ..
+                } if !is_extern => {
+                    let name = &self.typeenv.syms[name.index()];
+                    writeln!(
+                        code,
+                        "\n// Internal type {}: defined at {}.",
+                        name,
+                        pos.pretty_print_line(&self.typeenv.filename)
+                    )?;
+                    writeln!(code, "enum {} {{", name)?;
+                    for variant in variants {
+                        let name = &self.typeenv.syms[variant.name.index()];
+                        writeln!(code, "    {} {{", name)?;
+                        for field in &variant.fields {
+                            let name = &self.typeenv.syms[field.name.index()];
+                            let ty_name = self.typeenv.types[field.ty.index()].name(&self.typeenv);
+                            writeln!(code, "        {}: {},", name, ty_name)?;
+                        }
+                        writeln!(code, "    }}")?;
+                    }
+                    writeln!(code, "}}")?;
+                }
+                _ => {}
+            }
+        }
+        Ok(())
+    }
 }
diff --git a/cranelift/isle/src/lexer.rs b/cranelift/isle/src/lexer.rs
index eafb72a462..f9672db298 100644
--- a/cranelift/isle/src/lexer.rs
+++ b/cranelift/isle/src/lexer.rs
@@ -14,6 +14,15 @@ pub struct Pos {
     pub col: usize,
 }
 
+impl Pos {
+    pub fn pretty_print(&self, filename: &str) -> String {
+        format!("{}:{}:{}", filename, self.line, self.col)
+    }
+    pub fn pretty_print_line(&self, filename: &str) -> String {
+        format!("{} line {}", filename, self.line)
+    }
+}
+
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum Token<'a> {
     LParen,
diff --git a/cranelift/isle/src/sema.rs b/cranelift/isle/src/sema.rs
index 9e2bab9fe0..ff6a2d219e 100644
--- a/cranelift/isle/src/sema.rs
+++ b/cranelift/isle/src/sema.rs
@@ -50,7 +50,7 @@ pub enum Type {
 }
 
 impl Type {
-    fn name<'a>(&self, tyenv: &'a TypeEnv) -> &'a str {
+    pub fn name<'a>(&self, tyenv: &'a TypeEnv) -> &'a str {
         match self {
             Self::Primitive(_, name) | Self::Enum { name, .. } => &tyenv.syms[name.index()],
         }
@@ -60,6 +60,7 @@ impl Type {
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct Variant {
     pub name: Sym,
+    pub fullname: Sym,
     pub id: VariantId,
     pub fields: Vec<Field>,
 }
@@ -209,9 +210,10 @@ impl TypeEnv {
                 let mut variants = vec![];
                 for variant in ty_variants {
                     let combined_ident = ast::Ident(format!("{}.{}", ty.name.0, variant.name.0));
-                    let var_name = self.intern_mut(&combined_ident);
+                    let fullname = self.intern_mut(&combined_ident);
+                    let name = self.intern_mut(&variant.name);
                     let id = VariantId(variants.len());
-                    if variants.iter().any(|v: &Variant| v.name == var_name) {
+                    if variants.iter().any(|v: &Variant| v.name == name) {
                         return Err(self.error(
                             ty.pos,
                             format!("Duplicate variant name in type: '{}'", variant.name.0),
@@ -249,7 +251,8 @@ impl TypeEnv {
                         });
                     }
                     variants.push(Variant {
-                        name: var_name,
+                        name,
+                        fullname,
                         id,
                         fields,
                     });
@@ -376,12 +379,12 @@ impl TermEnv {
                     ..
                 } => {
                     for variant in variants {
-                        if self.term_map.contains_key(&variant.name) {
+                        if self.term_map.contains_key(&variant.fullname) {
                             return Err(tyenv.error(
                                 pos,
                                 format!(
                                     "Duplicate enum variant constructor: '{}'",
-                                    tyenv.syms[variant.name.index()]
+                                    tyenv.syms[variant.fullname.index()]
                                 ),
                             ));
                         }
@@ -390,14 +393,14 @@ impl TermEnv {
                         let ret_ty = id;
                         self.terms.push(Term {
                             id: tid,
-                            name: variant.name,
+                            name: variant.fullname,
                             arg_tys,
                             ret_ty,
                             kind: TermKind::EnumVariant {
                                 variant: variant.id,
                             },
                         });
-                        self.term_map.insert(variant.name, tid);
+                        self.term_map.insert(variant.fullname, tid);
                     }
                 }
                 _ => {}