diff --git a/spec/compiler/build_tables/next_symbols_spec.cpp b/spec/compiler/build_tables/next_symbols_spec.cpp
new file mode 100644
index 00000000..df932471
--- /dev/null
+++ b/spec/compiler/build_tables/next_symbols_spec.cpp
@@ -0,0 +1,38 @@
+#include "spec_helper.h"
+#include "build_tables/next_symbols.h"
+#include "grammar.h"
+#include "rules.h"
+
+using std::set;
+using namespace build_tables;
+using namespace rules;
+
+START_TEST
+
+describe("computing FIRST sets", []() {
+    Grammar grammar({
+        { "A", choice({
+            seq({
+                sym("B"),
+                sym("x"),
+                sym("B") }),
+            sym("B") }) },
+        { "B", choice({
+            seq({
+                sym("y"),
+                sym("z"),
+                sym("y") }),
+            sym("y") }) },
+    });
+    
+    describe("for a rule", [&]() {
+        it("searches the tree for terminals", [&]() {
+            auto terminals = next_terminals(grammar.rules.find("A")->second, grammar);
+            AssertThat(terminals, Equals(set<Symbol>({
+                Symbol("y")
+            })));
+        });
+    });
+});
+
+END_TEST
\ No newline at end of file
diff --git a/spec/spec_helper.h b/spec/spec_helper.h
index 1dec0ba0..8fce663e 100644
--- a/spec/spec_helper.h
+++ b/spec/spec_helper.h
@@ -4,6 +4,7 @@
 #include "bandit/bandit.h"
 #include <iostream>
 #include <unordered_set>
+#include <set>
 #include <unordered_map>
 #include "grammar.h"
 
@@ -26,7 +27,19 @@ namespace std {
         }
         return stream << ">";
     }
-    
+
+    template<typename T>
+    inline ostream& operator<<(ostream &stream, const set<T> &set) {
+        stream << string("#<set: ");
+        bool started = false;
+        for (auto item : set) {
+            if (started) stream << string(", ");
+            stream << item;
+            started = true;
+        }
+        return stream << ">";
+    }
+
     template<typename TKey, typename TValue>
     inline ostream& operator<<(ostream &stream, const unordered_map<TKey, TValue> &map) {
         stream << string("#<map: ");
diff --git a/src/compiler/build_tables/next_symbols.cpp b/src/compiler/build_tables/next_symbols.cpp
index f7969d90..fabe6531 100644
--- a/src/compiler/build_tables/next_symbols.cpp
+++ b/src/compiler/build_tables/next_symbols.cpp
@@ -6,28 +6,71 @@
 using std::set;
 using std::vector;
 using std::dynamic_pointer_cast;
+using namespace tree_sitter::rules;
 
 namespace tree_sitter {
-    class Grammar;
-    
     namespace build_tables {
-        template<bool isNonTerminal>
-        set<rules::Symbol> next_symbols(const Item &item, const Grammar &grammar) {
+        class FirstSetVisitor : Visitor {
+            set<Symbol> value;
+            const Grammar grammar;
+            
+            FirstSetVisitor(const Grammar &grammar) : grammar(grammar) {}
+            
+            set<Symbol> set_union(const set<Symbol> &left, const set<Symbol> &right) {
+                set<Symbol> result = left;
+                result.insert(right.begin(), right.end());
+                return result;
+            }
+            
+            void visit(const Symbol *rule) {
+                if (grammar.has_definition(*rule)) {
+                    value = apply(grammar.rule(rule->name), grammar);
+                } else {
+                    value = set<Symbol>({ *rule });
+                }
+            }
+            
+            void visit(const Choice *rule) {
+                value = set_union(apply(rule->left, grammar), apply(rule->right, grammar));
+            }
+            
+            void visit(const Seq *rule) {
+                value = apply(rule->left, grammar);
+            }
+
+        public:
+            static set<Symbol> apply(const rule_ptr rule, const Grammar &grammar) {
+                FirstSetVisitor visitor(grammar);
+                rule->accept(visitor);
+                return visitor.value;
+            }
+        };
+        
+        template<bool isTerminal>
+        set<rules::Symbol> next_symbols(const rules::rule_ptr &rule, const Grammar &grammar) {
             set<rules::Symbol> result;
-            for (auto pair : rule_transitions(item.rule)) {
+            for (auto pair : rule_transitions(rule)) {
                 auto symbol = dynamic_pointer_cast<const rules::Symbol>(pair.first);
-                if (symbol && (grammar.has_definition(*symbol) == isNonTerminal))
+                if (symbol && (grammar.has_definition(*symbol) == !isTerminal))
                     result.insert(*symbol);
             }
             return result;
         }
         
+        set<rules::Symbol> next_terminals(const rules::rule_ptr &rule, const Grammar &grammar) {
+            return FirstSetVisitor::apply(rule, grammar);
+        }
+
+        set<rules::Symbol> next_non_terminals(const rules::rule_ptr &rule, const Grammar &grammar) {
+            return next_symbols<false>(rule, grammar);
+        }
+
         set<rules::Symbol> next_terminals(const Item &item, const Grammar &grammar) {
-            return next_symbols<false>(item, grammar);
+            return next_terminals(item.rule, grammar);
         }
 
         set<rules::Symbol> next_non_terminals(const Item &item, const Grammar &grammar) {
-            return next_symbols<true>(item, grammar);
+            return next_non_terminals(item.rule, grammar);
         }
 
         set<rules::Symbol> next_terminals(const ItemSet &item_set, const Grammar &grammar) {
diff --git a/src/compiler/build_tables/next_symbols.h b/src/compiler/build_tables/next_symbols.h
index 719954e1..6818b525 100644
--- a/src/compiler/build_tables/next_symbols.h
+++ b/src/compiler/build_tables/next_symbols.h
@@ -9,6 +9,7 @@ namespace tree_sitter {
     class Grammar;
     
     namespace build_tables {
+        std::set<rules::Symbol> next_terminals(const rules::rule_ptr &rule, const Grammar &grammar);
         std::set<rules::Symbol> next_terminals(const ItemSet &item_set, const Grammar &grammar);
         std::set<rules::Symbol> next_terminals(const Item &item, const Grammar &grammar);
         std::set<rules::Symbol> next_non_terminals(const Item &item, const Grammar &grammar);
diff --git a/tree_sitter.xcodeproj/project.pbxproj b/tree_sitter.xcodeproj/project.pbxproj
index 4e504d37..56187eb1 100644
--- a/tree_sitter.xcodeproj/project.pbxproj
+++ b/tree_sitter.xcodeproj/project.pbxproj
@@ -18,6 +18,7 @@
 		1251209B1830145300C9B56A /* rule.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 1251209A1830145300C9B56A /* rule.cpp */; };
 		125120A4183083BD00C9B56A /* arithmetic.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 125120A3183083BD00C9B56A /* arithmetic.cpp */; };
 		12BC470518822B27005AC502 /* parse_config.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 12BC470318822A17005AC502 /* parse_config.cpp */; };
+		12BC470718830BC5005AC502 /* next_symbols_spec.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 12BC470618830BC5005AC502 /* next_symbols_spec.cpp */; };
 		12D136A4183678A2005F3369 /* repeat.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 12D136A2183678A2005F3369 /* repeat.cpp */; };
 		12EDCF8A187B498C005A7A07 /* tree_spec.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 12EDCF89187B498C005A7A07 /* tree_spec.cpp */; };
 		12EDCF8D187C6282005A7A07 /* document.c in Sources */ = {isa = PBXBuildFile; fileRef = 12EDCF8C187C6282005A7A07 /* document.c */; };
@@ -95,6 +96,7 @@
 		125120A218307FFD00C9B56A /* arithmetic.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = arithmetic.h; path = spec/fixtures/grammars/arithmetic.h; sourceTree = SOURCE_ROOT; };
 		125120A3183083BD00C9B56A /* arithmetic.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = arithmetic.cpp; path = spec/fixtures/grammars/arithmetic.cpp; sourceTree = SOURCE_ROOT; };
 		12BC470318822A17005AC502 /* parse_config.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = parse_config.cpp; sourceTree = "<group>"; };
+		12BC470618830BC5005AC502 /* next_symbols_spec.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = next_symbols_spec.cpp; sourceTree = "<group>"; };
 		12C344421822F27700B07BE3 /* transition_map.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = transition_map.h; path = ../build_tables/transition_map.h; sourceTree = "<group>"; };
 		12D1369E18342088005F3369 /* todo.md */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text; path = todo.md; sourceTree = "<group>"; };
 		12D136A0183570F5005F3369 /* pattern_spec.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = pattern_spec.cpp; path = spec/compiler/rules/pattern_spec.cpp; sourceTree = SOURCE_ROOT; };
@@ -229,6 +231,7 @@
 			children = (
 				12EDCFB6188205BA005A7A07 /* rule_transitions_spec.cpp */,
 				12EDCFB7188205BA005A7A07 /* perform_spec.cpp */,
+				12BC470618830BC5005AC502 /* next_symbols_spec.cpp */,
 			);
 			name = build_tables;
 			path = compiler/build_tables;
@@ -497,6 +500,7 @@
 				12EDCFBC188205BF005A7A07 /* rule_transitions_spec.cpp in Sources */,
 				12130605182C348F00FCF928 /* character.cpp in Sources */,
 				12EDCFB418820519005A7A07 /* compile.cpp in Sources */,
+				12BC470718830BC5005AC502 /* next_symbols_spec.cpp in Sources */,
 				1213060B182C389100FCF928 /* symbol.cpp in Sources */,
 				12EDCFB118820395005A7A07 /* item_set.cpp in Sources */,
 				1251209B1830145300C9B56A /* rule.cpp in Sources */,