diff --git a/lib/bundler/mirror.rb b/lib/bundler/mirror.rb
index 97a6776adb8..9903e158abb 100644
--- a/lib/bundler/mirror.rb
+++ b/lib/bundler/mirror.rb
@@ -37,7 +37,7 @@ def parse(key, value)
         mirror = if config.all?
           @all
         else
-          (@mirrors[config.uri] = @mirrors[config.uri] || Mirror.new)
+          @mirrors[config.uri] ||= Mirror.new
         end
         config.update_mirror(mirror)
       end
@@ -45,7 +45,8 @@ def parse(key, value)
     private
 
       def fetch_valid_mirror_for(uri)
-        mirror = (@mirrors[URI(uri.to_s.downcase)] || @mirrors[URI(uri.to_s).host] || Mirror.new(uri)).validate!(@prober)
+        mirror = @mirrors[uri.to_s.downcase] || @mirrors[URI(uri.to_s).host] || Mirror.new(uri)
+        mirror.validate!(@prober)
         mirror = Mirror.new(uri) unless mirror.valid?
         mirror
       end
@@ -71,7 +72,7 @@ def uri=(uri)
         @uri = if uri.nil?
           nil
         else
-          URI(uri.to_s)
+          URI(uri.to_s.downcase)
         end
         @valid = nil
       end
@@ -117,7 +118,7 @@ class MirrorConfig
 
       def initialize(config_line, value)
         uri, fallback =
-          config_line.match(%r{^mirror\.(all|.+?)(\.fallback_timeout)?\/?$}).captures
+          config_line.match(%r{\Amirror\.(all|.+?)(\.fallback_timeout)?\/?\z}).captures
         @fallback = !fallback.nil?
         @all = false
         if uri == "all"
diff --git a/lib/bundler/settings.rb b/lib/bundler/settings.rb
index 7339f721ada..3612023cb2c 100644
--- a/lib/bundler/settings.rb
+++ b/lib/bundler/settings.rb
@@ -140,7 +140,7 @@ def credentials_for(uri)
 
     def gem_mirrors
       all.inject(Mirrors.new) do |mirrors, k|
-        mirrors.parse(k, self[k]) if k =~ /^mirror\./
+        mirrors.parse(k, self[k]) if k.start_with?("mirror.")
         mirrors
       end
     end
@@ -321,16 +321,34 @@ def load_config(config_file)
       end
     end
 
+    PER_URI_OPTIONS = %w(
+      fallback_timeout
+    ).freeze
+
+    NORMALIZE_URI_OPTIONS_PATTERN =
+      /
+        \A
+        (\w+\.)? # optional prefix key
+        (https?.*?) # URI
+        (\.#{Regexp.union(PER_URI_OPTIONS)})? # optional suffix key
+        \z
+      /ix
+
     # TODO: duplicates Rubygems#normalize_uri
     # TODO: is this the correct place to validate mirror URIs?
     def self.normalize_uri(uri)
       uri = uri.to_s
-      uri = "#{uri}/" unless uri =~ %r{/\Z}
+      if uri =~ NORMALIZE_URI_OPTIONS_PATTERN
+        prefix = $1
+        uri = $2
+        suffix = $3
+      end
+      uri = "#{uri}/" unless uri.end_with?("/")
       uri = URI(uri)
       unless uri.absolute?
         raise ArgumentError, format("Gem sources must be absolute. You provided '%s'.", uri)
       end
-      uri
+      "#{prefix}#{uri}#{suffix}".downcase
     end
   end
 end
diff --git a/spec/bundler/settings_spec.rb b/spec/bundler/settings_spec.rb
index 020897882cb..ec018275004 100644
--- a/spec/bundler/settings_spec.rb
+++ b/spec/bundler/settings_spec.rb
@@ -251,6 +251,16 @@
         URI("http://rubygems-mirror.org/")
       )
     end
+
+    it "normalizes URIs with a fallback_timeout option" do
+      settings["mirror.https://rubygems.org/.fallback_timeout"] = "true"
+      expect(settings.all).to include("mirror.https://rubygems.org/.fallback_timeout")
+    end
+
+    it "normalizes URIs with a fallback_timeout option without a trailing slash" do
+      settings["mirror.https://rubygems.org.fallback_timeout"] = "true"
+      expect(settings.all).to include("mirror.https://rubygems.org/.fallback_timeout")
+    end
   end
 
   describe "BUNDLE_ keys format" do