diff --git a/gtsam/inference/LabeledSymbol.cpp b/gtsam/inference/LabeledSymbol.cpp
index 0d9c35d2c..6d34883fa 100644
--- a/gtsam/inference/LabeledSymbol.cpp
+++ b/gtsam/inference/LabeledSymbol.cpp
@@ -121,6 +121,13 @@ boost::function<bool(gtsam::Key)> LabeledSymbol::TypeLabelTest(unsigned char c,
   return boost::bind(&LabeledSymbol::chr,   boost::bind(make, _1)) == c &&
       boost::bind(&LabeledSymbol::label, boost::bind(make, _1)) == label;
 }
+
+/* ************************************************************************* */
+std::ostream &operator<<(std::ostream &os, const LabeledSymbol &symbol) {
+  os << StreamedKey(symbol);
+  return os;
+}
+
 /* ************************************************************************* */
 
 } // \namespace gtsam
diff --git a/gtsam/inference/LabeledSymbol.h b/gtsam/inference/LabeledSymbol.h
index 8c521b067..5b3ec8766 100644
--- a/gtsam/inference/LabeledSymbol.h
+++ b/gtsam/inference/LabeledSymbol.h
@@ -100,10 +100,15 @@ public:
   LabeledSymbol upper() const { return LabeledSymbol(c_, toupper(label_), j_); }
   LabeledSymbol lower() const { return LabeledSymbol(c_, tolower(label_), j_); }
 
-  // Create a new symbol with a different value
+  // Create a new symbol with a different character.
   LabeledSymbol newChr(unsigned char c) const { return LabeledSymbol(c, label_, j_); }
+
+  // Create a new symbol with a different label.
   LabeledSymbol newLabel(unsigned char label) const { return LabeledSymbol(c_, label, j_); }
 
+  /// Output stream operator that can be used with key_formatter (see Key.h).
+  friend std::ostream &operator<<(std::ostream &, const LabeledSymbol &);
+
 private:
 
   /** Serialization function */
diff --git a/gtsam/inference/tests/testLabeledSymbol.cpp b/gtsam/inference/tests/testLabeledSymbol.cpp
index b463f4131..2a56b39c2 100644
--- a/gtsam/inference/tests/testLabeledSymbol.cpp
+++ b/gtsam/inference/tests/testLabeledSymbol.cpp
@@ -80,6 +80,29 @@ TEST(LabeledSymbol, ChrTest) {
 }
 
 /* ************************************************************************* */
-int main() { TestResult tr; return TestRegistry::runAllTests(tr); }
+// A custom (nonsensical) formatter.
+string myFormatter(Key key) {
+  return "special";
+}
+
+TEST(LabeledSymbol, Formatting) {
+  LabeledSymbol symbol('c', 'A', 3);
+
+  // use key_formatter with a function pointer
+  stringstream ss2;
+  ss2 << key_formatter(myFormatter) << symbol;
+  EXPECT("special" == ss2.str());
+
+  // use key_formatter with a function object.
+  stringstream ss3;
+  ss3 << key_formatter(MultiRobotKeyFormatter) << symbol;
+  EXPECT("cA3" == ss3.str());
+}
+
+/* ************************************************************************* */
+int main() {
+  TestResult tr;
+  return TestRegistry::runAllTests(tr);
+}
 /* ************************************************************************* */