diff --git a/lib/tty/option/parser/param_types.rb b/lib/tty/option/parser/param_types.rb
index 347d3cc..2f17369 100644
--- a/lib/tty/option/parser/param_types.rb
+++ b/lib/tty/option/parser/param_types.rb
@@ -6,6 +6,7 @@ class Parser
       module ParamTypes
         # Positional argument pattern
         ARGUMENT_PARAMETER = /^[^-][^=]*\z/.freeze
+        ARGUMENT_HARDCODED_STRING = /\s/.freeze
 
         # Environment variable pattern
         ENV_VAR_PARAMETER = /^[\p{Lu}_\-\d]+=/.freeze
@@ -24,7 +25,8 @@ module ParamTypes
         #
         # @api public
         def argument?(value)
-          !value.match(ARGUMENT_PARAMETER).nil?
+          !value.match(ARGUMENT_PARAMETER).nil? ||
+            !value.match(ARGUMENT_HARDCODED_STRING).nil?
         end
 
         # Check if value is an environment variable
diff --git a/spec/unit/parse_spec.rb b/spec/unit/parse_spec.rb
index d6ed5b4..f08bf06 100644
--- a/spec/unit/parse_spec.rb
+++ b/spec/unit/parse_spec.rb
@@ -6,6 +6,15 @@
 
 RSpec.describe TTY::Option do
   context "argument" do
+    it "parses a hardcoded string with spaces as an argument" do
+      cmd = new_command do
+        argument :foo
+      end
+
+      cmd.parse(["bar TEST=something"])
+      expect(cmd.params[:foo]).to eq("bar TEST=something")
+    end
+
     it "doesn't allow to register same name parameter" do
       expect {
         command do
diff --git a/spec/unit/parser/param_types_spec.rb b/spec/unit/parser/param_types_spec.rb
index 128d03b..e4e0fd6 100644
--- a/spec/unit/parser/param_types_spec.rb
+++ b/spec/unit/parser/param_types_spec.rb
@@ -9,12 +9,13 @@ def type
 
   context "argument?" do
     {
-      "--foo"   => false,
-      "-f"      => false,
-      "foo=bar" => false,
-      "foo"     => true,
-      "f"       => true,
-      "FOO=bar" => false
+      "--foo"                   => false,
+      "-f"                      => false,
+      "foo=bar"                 => false,
+      "foo"                     => true,
+      "f"                       => true,
+      "FOO=bar"                 => false,
+      "something FOO=bar --foo" => true
     }.each do |input, result|
       it "returns #{result} for #{input.inspect}" do
         expect(type.argument?(input)).to eq(result)
@@ -24,13 +25,14 @@ def type
 
   context "env_var?" do
     {
-      "--foo"   => false,
-      "-f"      => false,
-      "foo=bar" => false,
-      "a=b"     => false,
-      "foo"     => false,
-      "FOO=bar" => true,
-      "A=b"     => true
+      "--foo"                   => false,
+      "-f"                      => false,
+      "foo=bar"                 => false,
+      "a=b"                     => false,
+      "foo"                     => false,
+      "FOO=bar"                 => true,
+      "A=b"                     => true,
+      "something FOO=bar --foo" => false
     }.each do |input, result|
       it "returns #{result} for #{input.inspect}" do
         expect(type.env_var?(input)).to eq(result)
@@ -40,13 +42,14 @@ def type
 
   context "keyword?" do
     {
-      "--foo"   => false,
-      "-f"      => false,
-      "-fa=b"   => false,
-      "foo=bar" => true,
-      "a=b"     => true,
-      "foo"     => false,
-      "FOO=bar" => false
+      "--foo"                   => false,
+      "-f"                      => false,
+      "-fa=b"                   => false,
+      "foo=bar"                 => true,
+      "a=b"                     => true,
+      "foo"                     => false,
+      "FOO=bar"                 => false,
+      "something FOO=bar --foo" => false
     }.each do |input, result|
       it "returns #{result} for #{input.inspect}" do
         expect(type.keyword?(input)).to eq(result)
@@ -56,12 +59,13 @@ def type
 
   context "option?" do
     {
-      "--foo"   => true,
-      "-f"      => true,
-      "foo=bar" => false,
-      "foo"     => false,
-      "f"       => false,
-      "FOO=bar" => false
+      "--foo"                   => true,
+      "-f"                      => true,
+      "foo=bar"                 => false,
+      "foo"                     => false,
+      "f"                       => false,
+      "FOO=bar"                 => false,
+      "something FOO=bar --foo" => false
     }.each do |input, result|
       it "returns #{result} for #{input.inspect}" do
         expect(type.option?(input)).to eq(result)