diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index fc663308d..da08f9638 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -16,15 +16,10 @@ jobs:
           - '3.0'
           - '2.7'
           - '2.6'
-          - '2.5'
           - head
           - truffleruby-head
         os: [ubuntu-latest]
         with_latest_reline: [true, false]
-        exclude:
-          - ruby: '2.5'
-            os: ubuntu-latest
-            with_latest_reline: true
       fail-fast: false
     runs-on: ${{ matrix.os }}
     env:
diff --git a/irb.gemspec b/irb.gemspec
index d44393804..c3e8a4dc5 100644
--- a/irb.gemspec
+++ b/irb.gemspec
@@ -34,7 +34,7 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
-  spec.required_ruby_version = Gem::Requirement.new(">= 2.5")
+  spec.required_ruby_version = Gem::Requirement.new(">= 2.6")
 
   spec.add_dependency "reline", ">= 0.3.0"
 end
diff --git a/lib/irb.rb b/lib/irb.rb
index 04009664e..ab5702c9f 100644
--- a/lib/irb.rb
+++ b/lib/irb.rb
@@ -598,11 +598,7 @@ def handle_exception(exc)
 
       if exc.backtrace
         order = nil
-        if '2.5.0' == RUBY_VERSION
-          # Exception#full_message doesn't have keyword arguments.
-          message = exc.full_message # the same of (highlight: true, order: bottom)
-          order = :bottom
-        elsif '2.5.1' <= RUBY_VERSION && RUBY_VERSION < '3.0.0'
+        if RUBY_VERSION < '3.0.0'
           if STDOUT.tty?
             message = exc.full_message(order: :bottom)
             order = :bottom
diff --git a/test/irb/test_context.rb b/test/irb/test_context.rb
index e127ba759..4d256a73a 100644
--- a/test/irb/test_context.rb
+++ b/test/irb/test_context.rb
@@ -492,7 +492,7 @@ def test_eval_input_with_exception
         irb.eval_input
       end
       assert_empty err
-      if '2.5.0' <= RUBY_VERSION && RUBY_VERSION < '3.0.0' && STDOUT.tty?
+      if RUBY_VERSION < '3.0.0' && STDOUT.tty?
         expected = [
           :*, /Traceback \(most recent call last\):\n/,
           :*, /\t 2: from \(irb\):1:in `<main>'\n/,
@@ -523,7 +523,7 @@ def test_eval_input_with_invalid_byte_sequence_exception
         irb.eval_input
       end
       assert_empty err
-      if '2.5.0' <= RUBY_VERSION && RUBY_VERSION < '3.0.0' && STDOUT.tty?
+      if RUBY_VERSION < '3.0.0' && STDOUT.tty?
         expected = [
           :*, /Traceback \(most recent call last\):\n/,
           :*, /\t 2: from \(irb\):1:in `<main>'\n/,
@@ -560,7 +560,7 @@ def test_eval_input_with_long_exception
         irb.eval_input
       end
       assert_empty err
-      if '2.5.0' <= RUBY_VERSION && RUBY_VERSION < '3.0.0' && STDOUT.tty?
+      if RUBY_VERSION < '3.0.0' && STDOUT.tty?
         expected = [
           :*, /Traceback \(most recent call last\):\n/,
           :*, /\t... \d+ levels...\n/,
diff --git a/test/irb/test_ruby_lex.rb b/test/irb/test_ruby_lex.rb
index 2b16e2e9a..fa68a4632 100644
--- a/test/irb/test_ruby_lex.rb
+++ b/test/irb/test_ruby_lex.rb
@@ -181,9 +181,6 @@ def test_symbols
     end
 
     def test_endless_range_at_end_of_line
-      if Gem::Version.new(RUBY_VERSION) < Gem::Version.new('2.6.0')
-        pend 'Endless range is available in 2.6.0 or later'
-      end
       input_with_prompt = [
         PromptRow.new('001:0: :> ', %q(a = 3..)),
         PromptRow.new('002:0: :* ', %q()),
diff --git a/test/lib/core_assertions.rb b/test/lib/core_assertions.rb
index bac3856a9..d8219ad71 100644
--- a/test/lib/core_assertions.rb
+++ b/test/lib/core_assertions.rb
@@ -694,8 +694,7 @@ def assert_join_threads(threads, message = nil)
         if !errs.empty?
           msg = "exceptions on #{errs.length} threads:\n" +
             errs.map {|t, err|
-            "#{t.inspect}:\n" +
-              RUBY_VERSION >= "2.5.0" ? err.full_message(highlight: false, order: :top) : err.message
+            "#{t.inspect}:\n" + err.full_message(highlight: false, order: :top)
           }.join("\n---\n")
           if message
             msg = "#{message}\n#{msg}"