diff --git a/crates/ailang-surface/src/print.rs b/crates/ailang-surface/src/print.rs
index b04ed8b..032ae43 100644
--- a/crates/ailang-surface/src/print.rs
+++ b/crates/ailang-surface/src/print.rs
@@ -8,8 +8,9 @@
 //! per level. Comments are NOT emitted.
 
 use ailang_core::ast::{
-    Arm, ClassDef, ClassMethod, ConstDef, Ctor, Def, FnDef, Import, InstanceDef, Literal,
-    Module, ParamMode, Pattern, SuperclassRef, Suppress, Term, Type, TypeDef,
+    Arm, ClassDef, ClassMethod, ConstDef, Ctor, Def, FnDef, Import, InstanceDef,
+    InstanceMethod, Literal, Module, ParamMode, Pattern, SuperclassRef, Suppress, Term,
+    Type, TypeDef,
 };
 
 /// Print a module in form (A).
@@ -274,9 +275,43 @@ fn write_class_method(out: &mut String, m: &ClassMethod, level: usize) {
     out.push(')');
 }
 
-fn write_instance_def(out: &mut String, _i: &InstanceDef, level: usize) {
+fn write_instance_def(out: &mut String, i: &InstanceDef, level: usize) {
     indent(out, level);
-    out.push_str("(instance)");
+    out.push_str("(instance");
+    out.push('\n');
+    indent(out, level + 1);
+    out.push_str("(class ");
+    out.push_str(&i.class);
+    out.push(')');
+    out.push('\n');
+    indent(out, level + 1);
+    out.push_str("(type ");
+    write_type(out, &i.type_);
+    out.push(')');
+    if let Some(doc) = &i.doc {
+        out.push('\n');
+        indent(out, level + 1);
+        out.push_str("(doc ");
+        write_string_lit(out, doc);
+        out.push(')');
+    }
+    for m in &i.methods {
+        out.push('\n');
+        write_instance_method(out, m, level + 1);
+    }
+    out.push(')');
+}
+
+fn write_instance_method(out: &mut String, m: &InstanceMethod, level: usize) {
+    indent(out, level);
+    out.push_str("(method ");
+    out.push_str(&m.name);
+    out.push('\n');
+    indent(out, level + 1);
+    out.push_str("(body ");
+    write_term(out, &m.body, level + 2);
+    out.push(')');
+    out.push(')');
 }
 
 // ---- types ----------------------------------------------------------------
@@ -622,4 +657,23 @@ mod tests {
         };
         round_trip(m, "class_with_superclass_and_default");
     }
+
+    #[test]
+    fn print_then_parse_round_trip_minimal_instance() {
+        let m = Module {
+            schema: ailang_core::SCHEMA.to_string(),
+            name: "M".into(),
+            imports: vec![],
+            defs: vec![Def::Instance(InstanceDef {
+                class: "Foo".into(),
+                type_: Type::int(),
+                methods: vec![InstanceMethod {
+                    name: "m".into(),
+                    body: Term::Lit { lit: Literal::Int { value: 5 } },
+                }],
+                doc: None,
+            })],
+        };
+        round_trip(m, "minimal_instance");
+    }
 }