diff --git a/eg/struct-equality.castile b/eg/struct-equality.castile
new file mode 100644
index 0000000..c327c0a
--- /dev/null
+++ b/eg/struct-equality.castile
@@ -0,0 +1,7 @@
+fun main() {
+  a = 40 as string|integer
+  b = 40 as string|integer
+  if a == b {
+    print("it is")
+  }
+}
diff --git a/src/castile/backends/c.py b/src/castile/backends/c.py
index 28e95a4..af5dce1 100644
--- a/src/castile/backends/c.py
+++ b/src/castile/backends/c.py
@@ -73,6 +73,11 @@
     return !strcmp(tag, tv->tag);
 }
 
+int equal_tagged_value(struct tagged_value *tv1, struct tagged_value *tv2)
+{
+    return is_tag(tv1->tag, tv2) && tv1->value == tv2->value;
+}
+
 """
 
 
@@ -262,6 +267,12 @@ def compile(self, ast):
                 self.write(', ')
                 self.compile(ast.children[1])
                 self.write(')')
+            elif ast.value == '==' and isinstance(ast.children[0].type, Union):
+                self.write('equal_tagged_value(')
+                self.compile(ast.children[0])
+                self.write(', ')
+                self.compile(ast.children[1])
+                self.write(')')
             else:
                 self.write('(')
                 self.compile(ast.children[0])
diff --git a/src/castile/builtins.py b/src/castile/builtins.py
index bc5bcd7..193ba2a 100644
--- a/src/castile/builtins.py
+++ b/src/castile/builtins.py
@@ -11,6 +11,9 @@ def __init__(self, tag, value):
     def __repr__(self):
         return '(%r, %r)' % (self.tag, self.value)
 
+    def __eq__(self, other):
+        return self.tag == other.tag and self.value == other.value
+
 
 def builtin_len(s):
     return len(s)
diff --git a/tests/Castile.md b/tests/Castile.md
index decae59..9067f26 100644
--- a/tests/Castile.md
+++ b/tests/Castile.md
@@ -601,16 +601,16 @@ Equality cannot be checked between two values of different types.
     | }
     ? mismatch
 
-Equality can be checked between unions.  (TODO)
-
-    /| fun main() {
-    /|   a = 40 as string|integer
-    /|   b = 40 as string|integer
-    /|   if a == b {
-    /|     print("it is")
-    /|   }
-    /| }
-    /= ok
+Equality can be checked between unions.
+
+    | fun main() {
+    |   a = 40 as string|integer
+    |   b = 40 as string|integer
+    |   if a == b {
+    |     print("it is")
+    |   }
+    | }
+    = it is
 
     | fun main() {
     |   a = 40 as string|integer