diff --git a/lib/linguist/heuristics.rb b/lib/linguist/heuristics.rb
index c1116780..fa5a97d7 100644
--- a/lib/linguist/heuristics.rb
+++ b/lib/linguist/heuristics.rb
@@ -1,7 +1,7 @@
 module Linguist
   # A collection of simple heuristics that can be used to better analyze languages.
   class Heuristics
-    ACTIVE = false
+    ACTIVE = true
 
     # Public: Given an array of String language names,
     # apply heuristics against the given data and return an array
@@ -12,26 +12,28 @@ module Linguist
     #
     # Returns an array of Languages or []
     def self.find_by_heuristics(data, languages)
+      determined = nil
       if active?
-        if languages.all? { |l| ["Objective-C", "C++"].include?(l) }
-          disambiguate_c(data, languages)
+        if languages.all? { |l| ["Objective-C", "C++", "C"].include?(l) }
+          determined = disambiguate_c(data, languages)
         end
         if languages.all? { |l| ["Perl", "Prolog"].include?(l) }
-          disambiguate_pl(data, languages)
+          determined = disambiguate_pl(data, languages)
         end
         if languages.all? { |l| ["ECL", "Prolog"].include?(l) }
-          disambiguate_ecl(data, languages)
+          determined = disambiguate_ecl(data, languages)
         end
         if languages.all? { |l| ["TypeScript", "XML"].include?(l) }
-          disambiguate_ts(data, languages)
+          determined = disambiguate_ts(data, languages)
         end
         if languages.all? { |l| ["Common Lisp", "OpenCL"].include?(l) }
-          disambiguate_cl(data, languages)
+          determined = disambiguate_cl(data, languages)
         end
         if languages.all? { |l| ["Rebol", "R"].include?(l) }
-          disambiguate_r(data, languages)
+          determined = disambiguate_r(data, languages)
         end
       end
+      determined
     end
 
     # .h extensions are ambigious between C, C++, and Objective-C.