diff --git a/test-suite/Cargo.toml b/test-suite/Cargo.toml
index 4f4db16..9f500b3 100644
--- a/test-suite/Cargo.toml
+++ b/test-suite/Cargo.toml
@@ -7,6 +7,6 @@ edition = "2018"
 
 [dev-dependencies]
 toml = { path = ".." }
-serde = "1.0"
+serde = { version = "1.0", features = ["derive"] }
 serde_derive = "1.0"
 serde_json = "1.0"
diff --git a/test-suite/tests/de-errors.rs b/test-suite/tests/de-errors.rs
new file mode 100644
index 0000000..d2e8f64
--- /dev/null
+++ b/test-suite/tests/de-errors.rs
@@ -0,0 +1,296 @@
+extern crate serde;
+extern crate toml;
+
+use serde::{de, Deserialize};
+use std::fmt;
+
+macro_rules! bad {
+    ($toml:expr, $ty:ty, $msg:expr) => {
+        match toml::from_str::<$ty>($toml) {
+            Ok(s) => panic!("parsed to: {:#?}", s),
+            Err(e) => assert_eq!(e.to_string(), $msg),
+        }
+    };
+}
+
+#[derive(Debug, Deserialize, PartialEq)]
+struct Parent<T> {
+    p_a: T,
+    p_b: Vec<Child<T>>,
+}
+
+#[derive(Debug, Deserialize, PartialEq)]
+#[serde(deny_unknown_fields)]
+struct Child<T> {
+    c_a: T,
+    c_b: T,
+}
+
+#[derive(Debug, PartialEq)]
+enum CasedString {
+    Lowercase(String),
+    Uppercase(String),
+}
+
+impl<'de> de::Deserialize<'de> for CasedString {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: de::Deserializer<'de>,
+    {
+        struct CasedStringVisitor;
+
+        impl<'de> de::Visitor<'de> for CasedStringVisitor {
+            type Value = CasedString;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("a string")
+            }
+
+            fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
+            where
+                E: de::Error,
+            {
+                if s.is_empty() {
+                    Err(de::Error::invalid_length(0, &"a non-empty string"))
+                } else if s.chars().all(|x| x.is_ascii_lowercase()) {
+                    Ok(CasedString::Lowercase(s.to_string()))
+                } else if s.chars().all(|x| x.is_ascii_uppercase()) {
+                    Ok(CasedString::Uppercase(s.to_string()))
+                } else {
+                    Err(de::Error::invalid_value(
+                        de::Unexpected::Str(s),
+                        &"all lowercase or all uppercase",
+                    ))
+                }
+            }
+        }
+
+        deserializer.deserialize_any(CasedStringVisitor)
+    }
+}
+
+#[test]
+fn custom_errors() {
+    toml::from_str::<Parent<CasedString>>(
+        "
+            p_a = 'a'
+            p_b = [{c_a = 'a', c_b = 'c'}]
+        ",
+    )
+    .unwrap();
+
+    // Custom error at p_b value.
+    bad!(
+        "
+            p_a = ''
+        ",
+        Parent<CasedString>,
+        "invalid length 0, expected a non-empty string for key `p_a`"
+    );
+
+    // Missing field in table.
+    bad!(
+        "
+            p_a = 'a'
+        ",
+        Parent<CasedString>,
+        "missing field `p_b`"
+    );
+
+    // Invalid type in p_b.
+    bad!(
+        "
+            p_a = 'a'
+            p_b = 1
+        ",
+        Parent<CasedString>,
+        "invalid type: integer `1`, expected a sequence for key `p_b`"
+    );
+
+    // Sub-table in Vec is missing a field.
+    bad!(
+        "
+            p_a = 'a'
+            p_b = [
+                {c_a = 'a'}
+            ]
+        ",
+        Parent<CasedString>,
+        "missing field `c_b` for key `p_b`"
+    );
+
+    // Sub-table in Vec has a field with a bad value.
+    bad!(
+        "
+            p_a = 'a'
+            p_b = [
+                {c_a = 'a', c_b = '*'}
+            ]
+        ",
+        Parent<CasedString>,
+        "invalid value: string \"*\", expected all lowercase or all uppercase for key `p_b`"
+    );
+
+    // Sub-table in Vec is missing a field.
+    bad!(
+        "
+            p_a = 'a'
+            p_b = [
+                {c_a = 'a', c_b = 'b'},
+                {c_a = 'aa'}
+            ]
+        ",
+        Parent<CasedString>,
+        "missing field `c_b` for key `p_b`"
+    );
+
+    // Sub-table in the middle of a Vec is missing a field.
+    bad!(
+        "
+            p_a = 'a'
+            p_b = [
+                {c_a = 'a', c_b = 'b'},
+                {c_a = 'aa'},
+                {c_a = 'aaa', c_b = 'bbb'},
+            ]
+        ",
+        Parent<CasedString>,
+        "missing field `c_b` for key `p_b`"
+    );
+
+    // Sub-table in the middle of a Vec has a field with a bad value.
+    bad!(
+        "
+            p_a = 'a'
+            p_b = [
+                {c_a = 'a', c_b = 'b'},
+                {c_a = 'aa', c_b = 1},
+                {c_a = 'aaa', c_b = 'bbb'},
+            ]
+        ",
+        Parent<CasedString>,
+        "invalid type: integer `1`, expected a string for key `p_b`"
+    );
+
+    // Sub-table in the middle of a Vec has an extra field.
+    bad!(
+        "
+            p_a = 'a'
+            p_b = [
+                {c_a = 'a', c_b = 'b'},
+                {c_a = 'aa', c_b = 'bb', c_d = 'd'},
+                {c_a = 'aaa', c_b = 'bbb'},
+            ]
+        ",
+        Parent<CasedString>,
+        "unknown field `c_d`, expected `c_a` or `c_b` for key `p_b`" // FIX ME
+    );
+
+    // Sub-table in the middle of a Vec is missing a field.
+    bad!(
+        "
+            p_a = 'a'
+            [[p_b]]
+            c_a = 'a'
+            c_b = 'b'
+            [[p_b]]
+            c_a = 'aa'
+            [[p_b]]
+            c_a = 'aaa'
+            c_b = 'bbb'
+        ",
+        Parent<CasedString>,
+        "missing field `c_b` for key `p_b`"
+    );
+
+    // Sub-table in the middle of a Vec has a field with a bad value.
+    bad!(
+        "
+            p_a = 'a'
+            [[p_b]]
+            c_a = 'a'
+            c_b = 'b'
+            [[p_b]]
+            c_a = 'aa'
+            c_b = '*'
+            [[p_b]]
+            c_a = 'aaa'
+            c_b = 'bbb'
+        ",
+        Parent<CasedString>,
+        "invalid value: string \"*\", expected all lowercase or all uppercase for key `p_b.c_b`"
+    );
+
+    // Sub-table in the middle of a Vec has an extra field.
+    bad!(
+        "
+            p_a = 'a'
+            [[p_b]]
+            c_a = 'a'
+            c_b = 'b'
+            [[p_b]]
+            c_a = 'aa'
+            c_d = 'dd' # unknown field
+            [[p_b]]
+            c_a = 'aaa'
+            c_b = 'bbb'
+        ",
+        Parent<CasedString>,
+        "unknown field `c_d`, expected `c_a` or `c_b` for key `p_b`"
+    );
+}
+
+#[test]
+fn serde_derive_deserialize_errors() {
+    bad!(
+        "
+            p_a = ''
+        ",
+        Parent<String>,
+        "missing field `p_b`"
+    );
+
+    bad!(
+        "
+            p_a = ''
+            p_b = [
+                {c_a = ''}
+            ]
+        ",
+        Parent<String>,
+        "missing field `c_b` for key `p_b`"
+    );
+
+    bad!(
+        "
+            p_a = ''
+            p_b = [
+                {c_a = '', c_b = 1}
+            ]
+        ",
+        Parent<String>,
+        "invalid type: integer `1`, expected a string for key `p_b`"
+    );
+
+    bad!(
+        "
+            p_a = ''
+            p_b = [
+                {c_a = '', c_b = '', c_d = ''},
+            ]
+        ",
+        Parent<String>,
+        "unknown field `c_d`, expected `c_a` or `c_b` for key `p_b`" // FIX ME
+    );
+
+    bad!(
+        "
+            p_a = 'a'
+            p_b = [
+                {c_a = '', c_b = 1, c_d = ''},
+            ]
+        ",
+        Parent<String>,
+        "invalid type: integer `1`, expected a string for key `p_b`"
+    );
+}