diff --git a/lib/puma/rack/backports/uri/common_18.rb b/lib/puma/rack/backports/uri/common_18.rb
index ca3a6360..bbe4fe07 100644
--- a/lib/puma/rack/backports/uri/common_18.rb
+++ b/lib/puma/rack/backports/uri/common_18.rb
@@ -7,22 +7,25 @@
 #
 
 module URI
-  TBLENCWWWCOMP_ = {} # :nodoc:
-  256.times do |i|
-    TBLENCWWWCOMP_[i.chr] = '%%%02X' % i
+  begin
+    TBLENCWWWCOMP_ = {} # :nodoc:
+    256.times do |i|
+      TBLENCWWWCOMP_[i.chr] = '%%%02X' % i
+    end
+    TBLENCWWWCOMP_[' '] = '+'
+    TBLENCWWWCOMP_.freeze
+    TBLDECWWWCOMP_ = {} # :nodoc:
+    256.times do |i|
+      h, l = i>>4, i&15
+      TBLDECWWWCOMP_['%%%X%X' % [h, l]] = i.chr
+      TBLDECWWWCOMP_['%%%x%X' % [h, l]] = i.chr
+      TBLDECWWWCOMP_['%%%X%x' % [h, l]] = i.chr
+      TBLDECWWWCOMP_['%%%x%x' % [h, l]] = i.chr
+    end
+    TBLDECWWWCOMP_['+'] = ' '
+    TBLDECWWWCOMP_.freeze
+  rescue Exception
   end
-  TBLENCWWWCOMP_[' '] = '+'
-  TBLENCWWWCOMP_.freeze
-  TBLDECWWWCOMP_ = {} # :nodoc:
-  256.times do |i|
-    h, l = i>>4, i&15
-    TBLDECWWWCOMP_['%%%X%X' % [h, l]] = i.chr
-    TBLDECWWWCOMP_['%%%x%X' % [h, l]] = i.chr
-    TBLDECWWWCOMP_['%%%X%x' % [h, l]] = i.chr
-    TBLDECWWWCOMP_['%%%x%x' % [h, l]] = i.chr
-  end
-  TBLDECWWWCOMP_['+'] = ' '
-  TBLDECWWWCOMP_.freeze
 
   # Encode given +s+ to URL-encoded form data.
   #
diff --git a/lib/puma/rack/backports/uri/common_192.rb b/lib/puma/rack/backports/uri/common_192.rb
index 1a0522bf..a3cc4d1d 100644
--- a/lib/puma/rack/backports/uri/common_192.rb
+++ b/lib/puma/rack/backports/uri/common_192.rb
@@ -17,17 +17,20 @@
 require 'uri/common'
 
 module URI
-  TBLDECWWWCOMP_ = {} unless const_defined?(:TBLDECWWWCOMP_)  #:nodoc:
-  if TBLDECWWWCOMP_.empty?
-    256.times do |i|
-      h, l = i>>4, i&15
-      TBLDECWWWCOMP_['%%%X%X' % [h, l]] = i.chr
-      TBLDECWWWCOMP_['%%%x%X' % [h, l]] = i.chr
-      TBLDECWWWCOMP_['%%%X%x' % [h, l]] = i.chr
-      TBLDECWWWCOMP_['%%%x%x' % [h, l]] = i.chr
+  begin
+    TBLDECWWWCOMP_ = {} unless const_defined?(:TBLDECWWWCOMP_)  #:nodoc:
+    if TBLDECWWWCOMP_.empty?
+      256.times do |i|
+        h, l = i>>4, i&15
+        TBLDECWWWCOMP_['%%%X%X' % [h, l]] = i.chr
+        TBLDECWWWCOMP_['%%%x%X' % [h, l]] = i.chr
+        TBLDECWWWCOMP_['%%%X%x' % [h, l]] = i.chr
+        TBLDECWWWCOMP_['%%%x%x' % [h, l]] = i.chr
+      end
+      TBLDECWWWCOMP_['+'] = ' '
+      TBLDECWWWCOMP_.freeze
     end
-    TBLDECWWWCOMP_['+'] = ' '
-    TBLDECWWWCOMP_.freeze
+  rescue Exception
   end
 
   def self.decode_www_form(str, enc=Encoding::UTF_8)
diff --git a/lib/puma/rack/backports/uri/common_193.rb b/lib/puma/rack/backports/uri/common_193.rb
index 2e582033..d4609d79 100644
--- a/lib/puma/rack/backports/uri/common_193.rb
+++ b/lib/puma/rack/backports/uri/common_193.rb
@@ -8,22 +8,26 @@ require 'uri/common'
 # Relevant commit:
 # https://github.com/ruby/ruby/commit/edb7cdf1eabaff78dfa5ffedfbc2e91b29fa9ca1
 
-module URI
-  256.times do |i|
-    TBLENCWWWCOMP_[i.chr] = '%%%02X' % i
-  end
-  TBLENCWWWCOMP_[' '] = '+'
-  TBLENCWWWCOMP_.freeze
 
-  256.times do |i|
-    h, l = i>>4, i&15
-    TBLDECWWWCOMP_['%%%X%X' % [h, l]] = i.chr
-    TBLDECWWWCOMP_['%%%x%X' % [h, l]] = i.chr
-    TBLDECWWWCOMP_['%%%X%x' % [h, l]] = i.chr
-    TBLDECWWWCOMP_['%%%x%x' % [h, l]] = i.chr
+module URI
+  begin
+    256.times do |i|
+      TBLENCWWWCOMP_[i.chr] = '%%%02X' % i
+    end
+    TBLENCWWWCOMP_[' '] = '+'
+    TBLENCWWWCOMP_.freeze
+
+    256.times do |i|
+      h, l = i>>4, i&15
+      TBLDECWWWCOMP_['%%%X%X' % [h, l]] = i.chr
+      TBLDECWWWCOMP_['%%%x%X' % [h, l]] = i.chr
+      TBLDECWWWCOMP_['%%%X%x' % [h, l]] = i.chr
+      TBLDECWWWCOMP_['%%%x%x' % [h, l]] = i.chr
+    end
+    TBLDECWWWCOMP_['+'] = ' '
+    TBLDECWWWCOMP_.freeze
+  rescue Exception
   end
-  TBLDECWWWCOMP_['+'] = ' '
-  TBLDECWWWCOMP_.freeze
 end
 
 # :startdoc: