diff --git a/changelog.md b/changelog.md
index 6cf7270..58e2f10 100644
--- a/changelog.md
+++ b/changelog.md
@@ -40,5 +40,7 @@
 * 2.8.3
    - Allow arbitrary atoms in record_opt_name()
 * 2.9.0
-   - Encode atom values for string types when not nil or null
+   - Encode atom values for string types when not `nil` or `null`
+* 2.9.1
+   - Add `true` and `false` to the atom exceptions when converting to strings
 
diff --git a/src/avro_primitive.erl b/src/avro_primitive.erl
index 9939cac..2bd60f6 100644
--- a/src/avro_primitive.erl
+++ b/src/avro_primitive.erl
@@ -121,10 +121,11 @@ cast(Type, Value) when ?IS_BYTES_TYPE(Type) andalso
 cast(Type, Value) when ?IS_STRING_TYPE(Type) andalso
                        (is_list(Value) orelse is_binary(Value)) ->
   {ok, ?AVRO_VALUE(Type, erlang:iolist_to_binary(Value))};
-% Encode atom values for string types when not null or nil
+% Encode atom values for string types when not null, nil, or booleans
 cast(Type, Value) when ?IS_STRING_TYPE(Type) andalso
                        (is_atom(Value) andalso
-                       (Value =/= null andalso Value =/= nil)) ->
+                       (Value =/= null andalso Value =/= nil andalso
+                        Value =/= true andalso Value =/= false)) ->
   {ok, ?AVRO_VALUE(Type, erlang:atom_to_binary(Value, utf8))};
 cast(Type, Value) -> {error, {type_mismatch, Type, Value}}.
 
diff --git a/src/erlavro.app.src b/src/erlavro.app.src
index 9110b7a..a2482f4 100644
--- a/src/erlavro.app.src
+++ b/src/erlavro.app.src
@@ -1,7 +1,7 @@
 {application, erlavro,
   [
     {description, "Apache Avro support for Erlang/Elixir"},
-    {vsn, "2.9.0"},
+    {vsn, "2.9.1"},
     {registered, []},
     {applications, [
       kernel,
diff --git a/test/avro_binary_encoder_tests.erl b/test/avro_binary_encoder_tests.erl
index 849aace..024e1fc 100644
--- a/test/avro_binary_encoder_tests.erl
+++ b/test/avro_binary_encoder_tests.erl
@@ -177,11 +177,17 @@ encode_map_error_test() ->
                encode(fun(_) -> error(unexpected) end, Type, Value)).
 
 encode_union_test() ->
-  Type = avro_union:type([null, string]),
+  Type = avro_union:type([null, string, boolean]),
   Value1 = avro_union:new(Type, null),
-  Value2 = avro_union:new(Type, "a"),
+  Value2 = avro_union:new(Type, nil),
+  Value3 = avro_union:new(Type, "a"),
+  Value4 = avro_union:new(Type, true),
+  Value5 = avro_union:new(Type, false),
   ?assertBinEq([0], encode_value(Value1)),
-  ?assertBinEq([long(1), long(1), 97], encode_value(Value2)).
+  ?assertBinEq([0], encode_value(Value2)),
+  ?assertBinEq([long(1), long(1), 97], encode_value(Value3)),
+  ?assertBinEq([long(2), <<1>>], encode_value(Value4)),
+  ?assertBinEq([long(2), <<0>>], encode_value(Value5)).
 
 encode_fixed_test() ->
   Type = avro_fixed:type("FooBar", 2),