diff --git a/lib/propane/rule_set.rb b/lib/propane/rule_set.rb
index d5911f0..ccdd5b0 100644
--- a/lib/propane/rule_set.rb
+++ b/lib/propane/rule_set.rb
@@ -119,6 +119,8 @@ class Propane
     def build_ast_fields(grammar)
       field_ast_node_indexes = {}
       field_indexes_across_all_rules = {}
+      # Stores the index into @ast_fields by field alias name.
+      field_aliases = {}
       @ast_fields = []
       @rules.each do |rule|
         rule.components.each_with_index do |component, i|
@@ -136,6 +138,16 @@ class Propane
             field_ast_node_indexes[field_name] = @ast_fields.size
             @ast_fields << {field_name => struct_name}
           end
+          rule.aliases.each do |alias_name, index|
+            if index == i
+              alias_ast_fields_index = field_ast_node_indexes[field_name]
+              if field_aliases[alias_name] && field_aliases[alias_name] != alias_ast_fields_index
+                raise Error.new("Error: conflicting AST node field positions for alias `#{alias_name}` in rule #{rule.name} defined on line #{rule.line_number}")
+              end
+              field_aliases[alias_name] = alias_ast_fields_index
+              @ast_fields[alias_ast_fields_index][alias_name] = @ast_fields[alias_ast_fields_index].first[1]
+            end
+          end
           field_indexes_across_all_rules[node_name] ||= Set.new
           field_indexes_across_all_rules[node_name] << field_ast_node_indexes[field_name]
           rule.rule_set_node_field_index_map[i] = field_ast_node_indexes[field_name]
@@ -150,18 +162,6 @@ class Propane
             "#{grammar.ast_prefix}#{node_name}#{grammar.ast_suffix}"
         end
       end
-      # Now merge in the field aliases as given by the user in the
-      # grammar.
-      field_aliases = {}
-      @rules.each do |rule|
-        rule.aliases.each do |alias_name, index|
-          if field_aliases[alias_name] && field_aliases[alias_name] != index
-            raise Error.new("Error: conflicting AST node field positions for alias `#{alias_name}` in rule #{rule.name} defined on line #{rule.line_number}")
-          end
-          field_aliases[alias_name] = index
-          @ast_fields[index][alias_name] = @ast_fields[index].first[1]
-        end
-      end
     end
 
   end
diff --git a/spec/propane_spec.rb b/spec/propane_spec.rb
index 6964bac..cc26092 100644
--- a/spec/propane_spec.rb
+++ b/spec/propane_spec.rb
@@ -1219,6 +1219,29 @@ EOF
         expect(results.status).to eq 0
       end
 
+      it "aliases the correct field when multiple rules are in a rule set in AST mode" do
+        write_grammar <<EOF
+ast;
+
+token a;
+token b;
+token c;
+drop /\\s+/;
+Start -> a;
+Start -> Foo;
+Start -> T:first T:second T:third;
+Foo -> b;
+T -> a;
+T -> b;
+T -> c;
+EOF
+        run_propane(language: language)
+        compile("spec/test_ast_field_aliases.#{language}", language: language)
+        results = run_test
+        expect(results.stderr).to eq ""
+        expect(results.status).to eq 0
+      end
+
       it "allows specifying field aliases when AST mode is not enabled" do
         if language == "d"
           write_grammar <<EOF
@@ -1253,6 +1276,56 @@ Start -> id:first id:second <<
   printf("first is %s\\n", ${first});
   printf("second is %s\\n", ${second});
 >>
+EOF
+        end
+        run_propane(language: language)
+        compile("spec/test_field_aliases.#{language}", language: language)
+        results = run_test
+        expect(results.stderr).to eq ""
+        expect(results.status).to eq 0
+        expect(results.stdout).to match /first is foo1.*second is bar2/m
+      end
+
+      it "aliases the correct field when multiple rules are in a rule set when AST mode is not enabled" do
+        if language == "d"
+          write_grammar <<EOF
+<<
+import std.stdio;
+>>
+ptype string;
+token id /[a-zA-Z_][a-zA-Z0-9_]*/ <<
+  $$ = match;
+>>
+drop /\\s+/;
+Start -> id;
+Start -> Foo;
+Start -> id:first id:second <<
+  writeln("first is ", ${first});
+  writeln("second is ", ${second});
+>>
+Foo -> ;
+EOF
+        else
+          write_grammar <<EOF
+<<
+#include <stdio.h>
+#include <string.h>
+>>
+ptype char const *;
+token id /[a-zA-Z_][a-zA-Z0-9_]*/ <<
+  char * s = malloc(match_length + 1);
+  strncpy(s, (char const *)match, match_length);
+  s[match_length] = 0;
+  $$ = s;
+>>
+drop /\\s+/;
+Start -> id;
+Start -> Foo;
+Start -> id:first id:second <<
+  printf("first is %s\\n", ${first});
+  printf("second is %s\\n", ${second});
+>>
+Foo -> ;
 EOF
         end
         run_propane(language: language)