diff --git a/lib/jsduck/ast.rb b/lib/jsduck/ast.rb
index 0f182991c5964b5a64424678ec90814c54b7b796..4374a29b691fbd1d7f51ce45da9e11101c350c30 100644
--- a/lib/jsduck/ast.rb
+++ b/lib/jsduck/ast.rb
@@ -8,10 +8,9 @@ module JsDuck
   # Analyzes the AST produced by EsprimaParser.
   class Ast
     # Should be initialized with EsprimaParser#parse result.
-    def initialize(docs = [], options = {})
+    def initialize(docs = [])
       @serializer = JsDuck::Serializer.new
       @evaluator = JsDuck::Evaluator.new
-      @ext_patterns = JsDuck::ExtPatterns.new(options[:ext_namespaces] || ["Ext"])
       @docs = docs
     end
 
@@ -174,7 +173,7 @@ module JsDuck
     end
 
     def ext_pattern?(pattern, ast)
-      @ext_patterns.matches?(pattern, to_s(ast))
+      ExtPatterns.matches?(pattern, to_s(ast))
     end
 
     def fire_event?(ast)
diff --git a/lib/jsduck/ext_patterns.rb b/lib/jsduck/ext_patterns.rb
index 2c59cc7f9ef268dc2687a4d7a44351d10ba4908c..147180c5b2a1da01e7c896a1e4ea45aa4813d988 100644
--- a/lib/jsduck/ext_patterns.rb
+++ b/lib/jsduck/ext_patterns.rb
@@ -1,3 +1,5 @@
+require "jsduck/util/singleton"
+
 module JsDuck
 
   # Identifies Ext JS builtins like Ext.define and Ext.extend, taking
@@ -15,17 +17,14 @@ module JsDuck
   # The matches? method will take care of identifying all these four
   # cases:
   #
-  #     ps = ExtPatterns.new(["Ext", "MyApp"])
-  #     matches?("Ext.define", "MyApp.define") --> true
+  #     ExtPatterns.set(["Ext", "MyApp"])
+  #     ExtPatterns.matches?("Ext.define", "MyApp.define") --> true
   #
   class ExtPatterns
-    def initialize(namespaces)
-      @patterns = {
-        "Ext.define" => build_patterns(namespaces, [".define", ".ClassManager.create"]),
-        "Ext.extend" => build_patterns(namespaces, [".extend"]),
-        "Ext.override" => build_patterns(namespaces, [".override"]),
-        "Ext.emptyFn" => build_patterns(namespaces, [".emptyFn"]),
-      }
+    include Util::Singleton
+
+    def initialize
+      set(["Ext"])
     end
 
     # True when string matches the given pattern type.
@@ -36,6 +35,17 @@ module JsDuck
       @patterns[pattern].include?(string)
     end
 
+    # Reconfigures ExtPatterns with different set of namespaces.
+    # Called when --ext-namespaces option is passed to JSDuck.
+    def set(namespaces)
+      @patterns = {
+        "Ext.define" => build_patterns(namespaces, [".define", ".ClassManager.create"]),
+        "Ext.extend" => build_patterns(namespaces, [".extend"]),
+        "Ext.override" => build_patterns(namespaces, [".override"]),
+        "Ext.emptyFn" => build_patterns(namespaces, [".emptyFn"]),
+      }
+    end
+
     private
 
     # Given Array of alternate Ext namespaces builds list of patterns
diff --git a/lib/jsduck/options.rb b/lib/jsduck/options.rb
index 23c4dda6bd1c3f95ca6c5b81b9b8e5dd9f4270c2..49638224b7badf88efb8633438e8cc1d7013649b 100644
--- a/lib/jsduck/options.rb
+++ b/lib/jsduck/options.rb
@@ -125,7 +125,6 @@ module JsDuck
       @data_path = nil # This gets assigned in JsDuck::WebWriter after writing the data file.
       @local_storage_db = "docs"
       @touch_examples_ui = false
-      @ext_namespaces = ["Ext"]
       @imports = []
       @new_since = nil
 
@@ -527,8 +526,8 @@ module JsDuck
           "In such case pass --ext-namespaces=Ext,YourNS option",
           "and JSDuck will recognize both Ext.define() and",
           "YourNs.define() plus few other things that depend on",
-          "Ext namespace like Ext.emptyFn.") do |ns|
-          @ext_namespaces = ns
+          "Ext namespace like Ext.emptyFn.") do |namespaces|
+          ExtPatterns.set(namespaces)
         end
 
         opts.on('--touch-examples-ui',
diff --git a/lib/jsduck/source/file_parser.rb b/lib/jsduck/source/file_parser.rb
index 01579f9dc8e759f3568fab99d01605d4c1125571..35938addfd79553404da48ec5d41b6f8da58cef6 100644
--- a/lib/jsduck/source/file_parser.rb
+++ b/lib/jsduck/source/file_parser.rb
@@ -43,7 +43,7 @@ module JsDuck
           docs = CssParser.new(contents, options).parse
         else
           docs = JsParser.new(contents, options).parse
-          docs = Ast.new(docs, options).detect_all!
+          docs = Ast.new(docs).detect_all!
         end
       end
 
diff --git a/spec/ext_namespaces_spec.rb b/spec/ext_namespaces_spec.rb
index d996ff867c81820af6055261cd8c9c84e112b0cc..0bcbd7e73f3f7e28e9522761ff3a81801e0fc693 100644
--- a/spec/ext_namespaces_spec.rb
+++ b/spec/ext_namespaces_spec.rb
@@ -1,10 +1,19 @@
 require "jsduck/js_parser"
 require "jsduck/ast"
+require "jsduck/ext_patterns"
 
 describe "--ext-namespaces=Ext,MyNs,MyNs.Foo.Bar" do
+  before do
+    JsDuck::ExtPatterns.set(["Ext", "MyNs", "MyNs.Foo.Bar"])
+  end
+
+  after do
+    JsDuck::ExtPatterns.set(["Ext"])
+  end
+
   def parse(string)
     docs = JsDuck::JsParser.new(string).parse
-    JsDuck::Ast.new(docs, {:ext_namespaces => ["Ext", "MyNs", "MyNs.Foo.Bar"]}).detect_all!
+    JsDuck::Ast.new(docs).detect_all!
   end
 
   it "allows detecting Ext.define()" do