diff --git a/src/human_encoding/error.rs b/src/human_encoding/error.rs
new file mode 100644
index 00000000..3cbcbef3
--- /dev/null
+++ b/src/human_encoding/error.rs
@@ -0,0 +1,217 @@
+// Simplicity "Human-Readable" Language
+//
+// To the extent possible under law, the author(s) have dedicated all
+// copyright and related and neighboring rights to this software to
+// the public domain worldwide. This software is distributed without
+// any warranty.
+//
+// You should have received a copy of the CC0 Public Domain Dedication
+// along with this software.
+// If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
+//
+
+//! Parsing Errors
+
+use std::collections::BTreeMap;
+use std::sync::{Arc, Mutex};
+use std::{error, fmt, iter};
+
+use crate::types;
+
+use super::Position;
+
+/// A set of errors found in a human-readable encoding of a Simplicity program.
+#[derive(Clone, Debug, Default)]
+pub struct ErrorSet {
+    context: Option<Arc<str>>,
+    line_map: Arc<Mutex<Vec<usize>>>,
+    errors: BTreeMap<Option<Position>, Vec<Error>>,
+}
+
+impl ErrorSet {
+    /// Constructs a new empty error set.
+    pub fn new() -> Self {
+        ErrorSet::default()
+    }
+
+    /// Returns the first (and presumably most important) error in the set, if it
+    /// is non-empty, along with its position.
+    pub fn first_error(&self) -> Option<(Option<Position>, &Error)> {
+        self.errors.iter().next().map(|(a, b)| (*a, &b[0]))
+    }
+
+    /// Constructs a new error set with a single error in it.
+    pub fn single<P: Into<Position>, E: Into<Error>>(position: P, err: E) -> Self {
+        let mut errors = BTreeMap::default();
+        errors.insert(Some(position.into()), vec![err.into()]);
+        ErrorSet {
+            context: None,
+            line_map: Arc::new(Mutex::new(vec![])),
+            errors,
+        }
+    }
+
+    /// Constructs a new error set with a single error in it.
+    pub fn single_no_position<E: Into<Error>>(err: E) -> Self {
+        let mut errors = BTreeMap::default();
+        errors.insert(None, vec![err.into()]);
+        ErrorSet {
+            context: None,
+            line_map: Arc::new(Mutex::new(vec![])),
+            errors,
+        }
+    }
+
+    /// Adds an error to the error set.
+    pub fn add<P: Into<Position>, E: Into<Error>>(&mut self, position: P, err: E) {
+        self.errors
+            .entry(Some(position.into()))
+            .or_insert(vec![])
+            .push(err.into());
+    }
+
+    /// Merges another set of errors into the current set.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the two sets have different contexts attached.
+    pub fn merge(&mut self, other: &Self) {
+        match (self.context.as_ref(), other.context.as_ref()) {
+            (None, None) => {}
+            (Some(_), None) => {}
+            (None, Some(b)) => self.context = Some(Arc::clone(b)),
+            (Some(a), Some(b)) => {
+                assert_eq!(a, b, "cannot merge error sets for different source input");
+            }
+        };
+
+        for (pos, errs) in &other.errors {
+            self.errors
+                .entry(*pos)
+                .or_insert(vec![])
+                .extend(errs.iter().cloned());
+        }
+    }
+
+    /// Attaches the input code to the error set, so that error messages can include
+    /// line numbers etc.
+    ///
+    /// # Panics
+    ///
+    /// Panics if it is called twice on the same error set. You should call this once
+    /// with the complete input code.
+    pub fn add_context(&mut self, s: Arc<str>) {
+        if self.context.is_some() {
+            panic!("tried to add context to the same error context twice");
+        }
+        self.context = Some(s);
+    }
+
+    /// Returns a boolean indicating whether the set is empty.
+    pub fn is_empty(&self) -> bool {
+        self.errors.is_empty()
+    }
+
+    /// Returns the number of errors currently in the set.
+    pub fn len(&self) -> usize {
+        self.errors.len()
+    }
+
+    /// Converts the error set into a result.
+    ///
+    /// If the set is empty, returns Ok with the given value. Otherwise
+    /// returns Err with itself.
+    pub fn into_result<T>(self, ok: T) -> Result<T, Self> {
+        if self.is_empty() {
+            Ok(ok)
+        } else {
+            Err(self)
+        }
+    }
+
+    /// Converts the error set into a result.
+    ///
+    /// If the set is empty, returns Ok with the result of calling the given closure.
+    /// Otherwise returns Err with itself.
+    pub fn into_result_with<T, F: FnOnce() -> T>(self, okfn: F) -> Result<T, Self> {
+        if self.is_empty() {
+            Ok(okfn())
+        } else {
+            Err(self)
+        }
+    }
+}
+
+impl error::Error for ErrorSet {
+    fn cause(&self) -> Option<&(dyn error::Error + 'static)> {
+        match self.first_error()?.1 {
+            Error::TypeCheck(ref e) => Some(e),
+        }
+    }
+}
+
+impl fmt::Display for ErrorSet {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let mut line_map = self.line_map.lock().unwrap();
+        if line_map.is_empty() {
+            if let Some(ref s) = self.context {
+                *line_map = iter::repeat(0)
+                    .take(2)
+                    .chain(
+                        s.char_indices()
+                            .filter_map(|(n, ch)| if ch == '\n' { Some(n) } else { None }),
+                    )
+                    .collect();
+            }
+        }
+
+        for (pos, errs) in &self.errors {
+            if let Some(pos) = pos {
+                for err in errs {
+                    if let Some(ref s) = self.context {
+                        let end = line_map.get(pos.line + 1).copied().unwrap_or(s.len());
+                        let line = &s[line_map[pos.line] + 1..end];
+                        writeln!(f, "{:5} | {}", pos.line, line)?;
+                        writeln!(f, "      | {:>width$}", "^", width = pos.column)?;
+                        writeln!(f, "      \\-- {}", err)?;
+                        writeln!(f)?;
+                    } else {
+                        writeln!(f, "{:4}:{:2}: {}", pos.line, pos.column, err,)?;
+                        writeln!(f)?;
+                    }
+                }
+            } else {
+                for err in errs {
+                    writeln!(f, "Error: {}", err)?;
+                }
+            }
+        }
+        Ok(())
+    }
+}
+
+/// An individual error.
+///
+/// Generally this structure should not be used on its own, but only wrapped in an
+/// [`ErrorSet`]. This is because in the human-readable encoding errors it is usually
+/// possible to continue past individual errors, and the user would prefer to see as
+/// many as possible at once.
+#[derive(Clone, Debug)]
+pub enum Error {
+    /// Simplicity type-checking error
+    TypeCheck(types::Error),
+}
+
+impl From<types::Error> for Error {
+    fn from(e: types::Error) -> Self {
+        Error::TypeCheck(e)
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            Error::TypeCheck(ref e) => fmt::Display::fmt(e, f),
+        }
+    }
+}
diff --git a/src/human_encoding/mod.rs b/src/human_encoding/mod.rs
index 855d4f95..39ccc1ba 100644
--- a/src/human_encoding/mod.rs
+++ b/src/human_encoding/mod.rs
@@ -20,6 +20,7 @@
 //! in a human-readable format.
 //!
 
+mod error;
 mod named_node;
 mod serialize;
 
@@ -31,6 +32,7 @@ use std::collections::HashMap;
 use std::str;
 use std::sync::Arc;
 
+pub use self::error::{Error, ErrorSet};
 pub use self::named_node::NamedCommitNode;
 
 /// Line/column pair