diff --git a/src/compiler.bbb b/src/compiler.bbb
index 7449493..d087d37 100644
--- a/src/compiler.bbb
+++ b/src/compiler.bbb
@@ -1407,6 +1407,22 @@ TypeAlias = struct
     line: u32,
 }
 
+UnionField = struct
+{
+    type: &Type,
+    name: []u8,
+    line: u32,
+}
+
+TypeUnion = struct
+{
+    fields: []UnionField,
+    byte_size: u64,
+    biggest_field: u64,
+    byte_alignment: u32,
+    line: u32,
+}
+
 TypeContent = union
 {
     integer: TypeInteger,
@@ -1418,6 +1434,7 @@ TypeContent = union
     struct: TypeStruct,
     bits: TypeBits,
     alias: TypeAlias,
+    union: TypeUnion,
 }
 
 TypeLLVM = struct
@@ -7115,7 +7132,88 @@ parse = fn (module: &Module) void
                     },
                     .union =>
                     {
-                        #trap();
+                        skip_space(module);
+                        expect_character(module, left_brace);
+
+                        >union_type: &Type = undefined;
+
+                        if (type_forward_declaration)
+                        {
+                            union_type = type_forward_declaration;
+                        }
+                        else
+                        {
+                            union_type = new_type(module, {
+                                .id = .forward_declaration,
+                                .name = global_name,
+                                .scope = &module.scope,
+                                zero,
+                            });
+                        }
+
+                        >field_count: u64 = 0;
+                        >biggest_field: u64 = 0;
+                        >alignment: u32 = 1;
+                        >byte_size: u64 = 0;
+
+                        >field_buffer: [64]UnionField = undefined;
+
+                        while (1)
+                        {
+                            skip_space(module);
+
+                            if (consume_character_if_match(module, right_brace))
+                            {
+                                break;
+                            }
+
+                            >field_index = field_count;
+                            field_count += 1;
+
+                            >field_line = get_line(module);
+                            >field_name = parse_identifier(module);
+
+                            skip_space(module);
+                            expect_character(module, ':');
+                            skip_space(module);
+
+                            >field_type = parse_type(module, scope);
+
+                            >field_alignment = get_byte_alignment(field_type);
+                            >field_size = get_byte_size(field_type);
+
+                            field_buffer[field_index] = {
+                                .type = field_type,
+                                .name = field_name,
+                                .line = field_line,
+                            };
+
+                            biggest_field = #select(field_size > byte_size, field_index, biggest_field);
+                            alignment = #max(alignment, field_alignment);
+                            byte_size = #max(byte_size, field_size);
+
+                            skip_space(module);
+
+                            consume_character_if_match(module, ',');
+                        }
+
+                        skip_space(module);
+                        consume_character_if_match(module, ';');
+
+                        >fields = arena_allocate_slice[UnionField](module.arena, field_count);
+                        memcpy(#pointer_cast(fields.pointer), #pointer_cast(&field_buffer), field_count * #byte_size(UnionField));
+
+                        >biggest_size = get_byte_size(fields[biggest_field].type);
+                        assert(biggest_size == byte_size);
+
+                        union_type.content.union = {
+                            .fields = fields,
+                            .byte_size = byte_size,
+                            .byte_alignment = alignment,
+                            .line = global_line,
+                            .biggest_field = biggest_field,
+                        };
+                        union_type.id = .union;
                     },
                 }
             }
@@ -15903,6 +16001,7 @@ names: [_][]u8 =
     "integer_formats",
     "for_each_int",
     "bool_array",
+    "basic_union",
 ];
 
 [export] main = fn [cc(c)] (argument_count: u32, argv: &&u8, envp: &&u8) s32