diff --git a/actionpack/lib/action_dispatch/journey/gtg/builder.rb b/actionpack/lib/action_dispatch/journey/gtg/builder.rb
index 7d2791714b..450588cda6 100644
--- a/actionpack/lib/action_dispatch/journey/gtg/builder.rb
+++ b/actionpack/lib/action_dispatch/journey/gtg/builder.rb
@@ -27,7 +27,7 @@ module ActionDispatch
             marked[s] = true # mark s
 
             s.group_by { |state| symbol(state) }.each do |sym, ps|
-              u = ps.map { |l| followpos(l) }.flatten
+              u = ps.flat_map { |l| followpos(l) }
               next if u.empty?
 
               if u.uniq == [DUMMY]
@@ -90,7 +90,7 @@ module ActionDispatch
               firstpos(node.left)
             end
           when Nodes::Or
-            node.children.map { |c| firstpos(c) }.flatten.uniq
+            node.children.flat_map { |c| firstpos(c) }.uniq
           when Nodes::Unary
             firstpos(node.left)
           when Nodes::Terminal
@@ -105,7 +105,7 @@ module ActionDispatch
           when Nodes::Star
             firstpos(node.left)
           when Nodes::Or
-            node.children.map { |c| lastpos(c) }.flatten.uniq
+            node.children.flat_map { |c| lastpos(c) }.uniq
           when Nodes::Cat
             if nullable?(node.right)
               lastpos(node.left) | lastpos(node.right)
diff --git a/actionpack/lib/action_dispatch/journey/gtg/simulator.rb b/actionpack/lib/action_dispatch/journey/gtg/simulator.rb
index 58ad803841..254c2befc4 100644
--- a/actionpack/lib/action_dispatch/journey/gtg/simulator.rb
+++ b/actionpack/lib/action_dispatch/journey/gtg/simulator.rb
@@ -31,7 +31,7 @@ module ActionDispatch
 
           return if acceptance_states.empty?
 
-          memos = acceptance_states.map { |x| tt.memo(x) }.flatten.compact
+          memos = acceptance_states.flat_map { |x| tt.memo(x) }.compact
 
           MatchData.new(memos)
         end
diff --git a/actionpack/lib/action_dispatch/journey/gtg/transition_table.rb b/actionpack/lib/action_dispatch/journey/gtg/transition_table.rb
index a5b19fcf06..e6212b1ee2 100644
--- a/actionpack/lib/action_dispatch/journey/gtg/transition_table.rb
+++ b/actionpack/lib/action_dispatch/journey/gtg/transition_table.rb
@@ -114,8 +114,8 @@ module ActionDispatch
         end
 
         def states
-          ss = @string_states.keys + @string_states.values.map(&:values).flatten
-          rs = @regexp_states.keys + @regexp_states.values.map(&:values).flatten
+          ss = @string_states.keys + @string_states.values.flat_map(&:values)
+          rs = @regexp_states.keys + @regexp_states.values.flat_map(&:values)
           (ss + rs).uniq
         end
 
@@ -143,11 +143,11 @@ module ActionDispatch
           def move_regexp(t, a)
             return [] if t.empty?
 
-            t.map { |s|
+            t.flat_map { |s|
               if states = @regexp_states[s]
                 states.map { |re, v| re === a ? v : nil }
               end
-            }.flatten.compact.uniq
+            }.compact.uniq
           end
 
           def move_string(t, a)
diff --git a/actionpack/lib/action_dispatch/journey/nfa/dot.rb b/actionpack/lib/action_dispatch/journey/nfa/dot.rb
index 5c33a872e5..47bf76bdbf 100644
--- a/actionpack/lib/action_dispatch/journey/nfa/dot.rb
+++ b/actionpack/lib/action_dispatch/journey/nfa/dot.rb
@@ -16,9 +16,9 @@ module ActionDispatch
           #  end
           #  "  #{n.object_id} [label=\"#{label}\", shape=box];"
           #}
-          #memo_edges = memos.map { |k, memos|
+          #memo_edges = memos.flat_map { |k, memos|
           #  (memos || []).map { |v| "  #{k} -> #{v.object_id};" }
-          #}.flatten.uniq
+          #}.uniq
 
         <<-eodot
 digraph nfa {
diff --git a/actionpack/lib/action_dispatch/journey/nfa/simulator.rb b/actionpack/lib/action_dispatch/journey/nfa/simulator.rb
index 5b40da6569..b23270db3c 100644
--- a/actionpack/lib/action_dispatch/journey/nfa/simulator.rb
+++ b/actionpack/lib/action_dispatch/journey/nfa/simulator.rb
@@ -34,7 +34,7 @@ module ActionDispatch
 
           return if acceptance_states.empty?
 
-          memos = acceptance_states.map { |x| tt.memo(x) }.flatten.compact
+          memos = acceptance_states.flat_map { |x| tt.memo(x) }.compact
 
           MatchData.new(memos)
         end
diff --git a/actionpack/lib/action_dispatch/journey/nfa/transition_table.rb b/actionpack/lib/action_dispatch/journey/nfa/transition_table.rb
index a3017aeea1..66e414213a 100644
--- a/actionpack/lib/action_dispatch/journey/nfa/transition_table.rb
+++ b/actionpack/lib/action_dispatch/journey/nfa/transition_table.rb
@@ -42,7 +42,7 @@ module ActionDispatch
         end
 
         def states
-          (@table.keys + @table.values.map(&:keys).flatten).uniq
+          (@table.keys + @table.values.flat_map(&:keys)).uniq
         end
 
         # Returns a generalized transition graph with reduced states. The states
@@ -93,7 +93,7 @@ module ActionDispatch
         # Returns set of NFA states to which there is a transition on ast symbol
         # +a+ from some state +s+ in +t+.
         def following_states(t, a)
-          Array(t).map { |s| inverted[s][a] }.flatten.uniq
+          Array(t).flat_map { |s| inverted[s][a] }.uniq
         end
 
         # Returns set of NFA states to which there is a transition on ast symbol
@@ -107,7 +107,7 @@ module ActionDispatch
         end
 
         def alphabet
-          inverted.values.map(&:keys).flatten.compact.uniq.sort_by { |x| x.to_s }
+          inverted.values.flat_map(&:keys).compact.uniq.sort_by { |x| x.to_s }
         end
 
         # Returns a set of NFA states reachable from some NFA state +s+ in set
@@ -131,9 +131,9 @@ module ActionDispatch
         end
 
         def transitions
-          @table.map { |to, hash|
+          @table.flat_map { |to, hash|
             hash.map { |from, sym| [from, sym, to] }
-          }.flatten(1)
+          }
         end
 
         private
diff --git a/actionpack/lib/action_dispatch/journey/path/pattern.rb b/actionpack/lib/action_dispatch/journey/path/pattern.rb
index d37aa1fbe5..fb155e516f 100644
--- a/actionpack/lib/action_dispatch/journey/path/pattern.rb
+++ b/actionpack/lib/action_dispatch/journey/path/pattern.rb
@@ -53,9 +53,9 @@ module ActionDispatch
         end
 
         def optional_names
-          @optional_names ||= spec.grep(Nodes::Group).map { |group|
+          @optional_names ||= spec.grep(Nodes::Group).flat_map { |group|
             group.grep(Nodes::Symbol)
-          }.flatten.map { |n| n.name }.uniq
+          }.map { |n| n.name }.uniq
         end
 
         class RegexpOffsets < Journey::Visitors::Visitor # :nodoc: