diff --git a/tvix/eval/src/compiler/mod.rs b/tvix/eval/src/compiler/mod.rs
index 6a3d10acf..d69566f07 100644
--- a/tvix/eval/src/compiler/mod.rs
+++ b/tvix/eval/src/compiler/mod.rs
@@ -28,7 +28,7 @@ use std::sync::Arc;
 
 use crate::chunk::Chunk;
 use crate::errors::{Error, ErrorKind, EvalResult};
-use crate::observer::Observer;
+use crate::observer::CompilerObserver;
 use crate::opcode::{CodeIdx, Count, JumpOffset, OpCode, UpvalueIdx};
 use crate::value::{Closure, Lambda, Thunk, Value};
 use crate::warnings::{EvalWarning, WarningKind};
@@ -95,7 +95,7 @@ struct Compiler<'observer> {
 
     /// Carry an observer for the compilation process, which is called
     /// whenever a chunk is emitted.
-    observer: &'observer mut dyn Observer,
+    observer: &'observer mut dyn CompilerObserver,
 }
 
 /// Compiler construction
@@ -104,7 +104,7 @@ impl<'observer> Compiler<'observer> {
         location: Option<PathBuf>,
         file: Arc<codemap::File>,
         globals: HashMap<&'static str, Value>,
-        observer: &'observer mut dyn Observer,
+        observer: &'observer mut dyn CompilerObserver,
     ) -> EvalResult<Self> {
         let mut root_dir = match location {
             Some(dir) => Ok(dir),
@@ -1146,7 +1146,7 @@ pub fn compile(
     location: Option<PathBuf>,
     file: Arc<codemap::File>,
     globals: HashMap<&'static str, Value>,
-    observer: &mut dyn Observer,
+    observer: &mut dyn CompilerObserver,
 ) -> EvalResult<CompilationOutput> {
     let mut c = Compiler::new(location, file, globals, observer)?;
 
diff --git a/tvix/eval/src/observer.rs b/tvix/eval/src/observer.rs
index e5562e369..ce237529f 100644
--- a/tvix/eval/src/observer.rs
+++ b/tvix/eval/src/observer.rs
@@ -1,9 +1,11 @@
-//! Implements a trait for things that wish to observe internal state
+//! Implements traits for things that wish to observe internal state
 //! changes of tvix-eval.
 //!
 //! This can be used to gain insights from compilation, to trace the
 //! runtime, and so on.
-
+//!
+//! All methods are optional, that is, observers can implement only
+/// what they are interested in observing.
 use codemap::CodeMap;
 use std::io::Write;
 use std::rc::Rc;
@@ -15,11 +17,8 @@ use crate::value::Lambda;
 use crate::Value;
 
 /// Implemented by types that wish to observe internal happenings of
-/// Tvix.
-///
-/// All methods are optional, that is, observers can implement only
-/// what they are interested in observing.
-pub trait Observer {
+/// the Tvix compiler.
+pub trait CompilerObserver {
     /// Called when the compiler finishes compilation of the top-level
     /// of an expression (usually the root Nix expression of a file).
     fn observe_compiled_toplevel(&mut self, _: &Rc<Lambda>) {}
@@ -34,7 +33,11 @@ pub trait Observer {
 
     /// Called when the compiler finishes compilation of a thunk.
     fn observe_compiled_thunk(&mut self, _: &Rc<Lambda>) {}
+}
 
+/// Implemented by types that wish to observe internal happenings of
+/// the Tvix virtual machine at runtime.
+pub trait RuntimeObserver {
     /// Called when the runtime enters a new call frame.
     fn observe_enter_frame(&mut self, _arg_count: usize, _: &Rc<Lambda>, _call_depth: usize) {}
 
@@ -59,7 +62,8 @@ pub trait Observer {
 #[derive(Default)]
 pub struct NoOpObserver {}
 
-impl Observer for NoOpObserver {}
+impl CompilerObserver for NoOpObserver {}
+impl RuntimeObserver for NoOpObserver {}
 
 /// An observer that prints disassembled chunk information to its
 /// internal writer whenwever the compiler emits a toplevel function,
@@ -97,7 +101,7 @@ impl<W: Write> DisassemblingObserver<W> {
     }
 }
 
-impl<W: Write> Observer for DisassemblingObserver<W> {
+impl<W: Write> CompilerObserver for DisassemblingObserver<W> {
     fn observe_compiled_toplevel(&mut self, lambda: &Rc<Lambda>) {
         self.lambda_header("toplevel", lambda);
         self.disassemble_chunk(&lambda.chunk);
@@ -131,7 +135,7 @@ impl<W: Write> TracingObserver<W> {
     }
 }
 
-impl<W: Write> Observer for TracingObserver<W> {
+impl<W: Write> RuntimeObserver for TracingObserver<W> {
     fn observe_enter_frame(&mut self, arg_count: usize, lambda: &Rc<Lambda>, call_depth: usize) {
         let _ = writeln!(
             &mut self.writer,
diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs
index 39c9c6e82..41f51a987 100644
--- a/tvix/eval/src/vm.rs
+++ b/tvix/eval/src/vm.rs
@@ -6,7 +6,7 @@ use std::{cell::RefMut, rc::Rc};
 use crate::{
     chunk::Chunk,
     errors::{Error, ErrorKind, EvalResult},
-    observer::Observer,
+    observer::RuntimeObserver,
     opcode::{CodeIdx, Count, JumpOffset, OpCode, StackIdx, UpvalueIdx},
     upvalues::{UpvalueCarrier, Upvalues},
     value::{Builtin, Closure, CoercionKind, Lambda, NixAttrs, NixList, Thunk, Value},
@@ -43,7 +43,7 @@ pub struct VM<'o> {
     /// dynamically resolved (`with`).
     with_stack: Vec<usize>,
 
-    observer: &'o mut dyn Observer,
+    observer: &'o mut dyn RuntimeObserver,
 }
 
 /// This macro wraps a computation that returns an ErrorKind or a
@@ -127,7 +127,7 @@ macro_rules! cmp_op {
 }
 
 impl<'o> VM<'o> {
-    pub fn new(observer: &'o mut dyn Observer) -> Self {
+    pub fn new(observer: &'o mut dyn RuntimeObserver) -> Self {
         Self {
             observer,
             frames: vec![],
@@ -780,7 +780,7 @@ fn unwrap_or_clone_rc<T: Clone>(rc: Rc<T>) -> T {
     Rc::try_unwrap(rc).unwrap_or_else(|rc| (*rc).clone())
 }
 
-pub fn run_lambda(observer: &mut dyn Observer, lambda: Rc<Lambda>) -> EvalResult<Value> {
+pub fn run_lambda(observer: &mut dyn RuntimeObserver, lambda: Rc<Lambda>) -> EvalResult<Value> {
     let mut vm = VM::new(observer);
     let value = vm.call(lambda, Upvalues::with_capacity(0), 0)?;
     vm.force_for_output(&value)?;