diff --git a/lib/tty/prompt/list.rb b/lib/tty/prompt/list.rb
index 81f335b7..cab8b9c8 100644
--- a/lib/tty/prompt/list.rb
+++ b/lib/tty/prompt/list.rb
@@ -143,6 +143,10 @@ def setup_defaults
       # @api private
       def validate_defaults
         @default.each do |d|
+          if d.nil? || d.to_s.empty?
+            fail ConfigurationError,
+                 "default index must be an integer in range (1 - #{@choices.size})"
+          end
           if d < 1 || d > @choices.size
             fail ConfigurationError,
                  "default index `#{d}` out of range (1 - #{@choices.size})"
diff --git a/spec/unit/select_spec.rb b/spec/unit/select_spec.rb
index 4f87074e..424c9b7c 100644
--- a/spec/unit/select_spec.rb
+++ b/spec/unit/select_spec.rb
@@ -193,4 +193,26 @@
       "[?] What size? \e[32mLarge\e[0m\n\e[?25h"
     ].join)
   end
+
+  it "verifies default index format" do
+    prompt = TTY::TestPrompt.new
+    choices = %w(Large Medium Small)
+    prompt.input << "\r"
+    prompt.input.rewind
+
+    expect {
+      prompt.select('What size?', choices, default: '')
+    }.to raise_error(TTY::Prompt::ConfigurationError, /in range \(1 - 3\)/)
+  end
+
+  it "verifies default index range" do
+    prompt = TTY::TestPrompt.new
+    choices = %w(Large Medium Small)
+    prompt.input << "\r"
+    prompt.input.rewind
+
+    expect {
+      prompt.select('What size?', choices, default: 10)
+    }.to raise_error(TTY::Prompt::ConfigurationError, /`10` out of range \(1 - 3\)/)
+  end
 end