diff --git a/src/LR0.cpp b/src/LR0.cpp
index a0ecac2c..5d174678 100644
--- a/src/LR0.cpp
+++ b/src/LR0.cpp
@@ -116,13 +116,12 @@ LR0::Closure LR0::getClosure (const Closure& items)
 
 ////////////////////////////////////////////////////////////////////////////////
 // Collect a unique set of expected symbols from the closure.
-std::vector <std::string> LR0::getExpected (const Closure& closure)
+std::set <std::string> LR0::getExpected (const Closure& closure)
 {
-  std::vector <std::string> expected;
+  std::set <std::string> expected;
   for (auto& item : closure)
-    if (! item.done () &&
-        std::find (expected.begin (), expected.end (), item.next ()) == expected.end ())
-      expected.push_back (item.next ());
+    if (! item.done ())
+      expected.insert (item.next ());
 
   return expected;
 }
diff --git a/src/LR0.h b/src/LR0.h
index ae7635ff..cdaa2d80 100644
--- a/src/LR0.h
+++ b/src/LR0.h
@@ -28,6 +28,7 @@
 #define INCLUDED_LR0
 
 #include <Grammar.h>
+#include <set>
 #include <map>
 #include <string>
 
@@ -68,7 +69,7 @@ public:
 
 private:
   Closure getClosure (const Closure&);
-  std::vector <std::string> getExpected (const Closure&);
+  std::set <std::string> getExpected (const Closure&);
 
 private:
   // Copy of the augmented grammar.