diff --git a/core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/UndefinedPattern.java b/core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/UndefinedPattern.java
new file mode 100644
index 00000000..ae965de3
--- /dev/null
+++ b/core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/UndefinedPattern.java
@@ -0,0 +1,25 @@
+package it.cavallium.warppi.math.rules.dsl.patterns;
+
+import it.cavallium.warppi.math.Function;
+import it.cavallium.warppi.math.MathContext;
+import it.cavallium.warppi.math.functions.Undefined;
+import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+/**
+ * Matches and generates <code>Undefined</code>.
+ */
+public class UndefinedPattern extends VisitorPattern {
+    @Override
+    public Optional<Map<String, Function>> visit(Undefined undefined) {
+        return Optional.of(new HashMap<>());
+    }
+
+    @Override
+    public Function replace(MathContext mathContext, Map<String, Function> subFunctions) {
+        return new Undefined(mathContext);
+    }
+}
diff --git a/core/src/test/java/it/cavallium/warppi/math/rules/dsl/PatternTest.java b/core/src/test/java/it/cavallium/warppi/math/rules/dsl/PatternTest.java
index 481e4bd2..a8f76b19 100644
--- a/core/src/test/java/it/cavallium/warppi/math/rules/dsl/PatternTest.java
+++ b/core/src/test/java/it/cavallium/warppi/math/rules/dsl/PatternTest.java
@@ -115,6 +115,19 @@ public class PatternTest {
         assertEquals(shouldMatch, pattern.replace(mathContext, subFunctions.get()));
     }
 
+    @Test
+    public void undefinedPattern() {
+        final Pattern pattern = new UndefinedPattern();
+
+        final Function shouldNotMatch = new Number(mathContext, 0);
+        assertFalse(pattern.match(shouldNotMatch).isPresent());
+
+        final Function shouldMatch = new Undefined(mathContext);
+        final Optional<Map<String, Function>> subFunctions = pattern.match(shouldMatch);
+        assertTrue(subFunctions.isPresent());
+        assertTrue(pattern.replace(mathContext, subFunctions.get()) instanceof Undefined);
+    }
+
     @Test
     public void otherBinaryPatterns() {
         final Number one = new Number(mathContext, 1);