diff --git a/lib/rouge/demos/gnuasm b/lib/rouge/demos/gnuasm
new file mode 100644
index 0000000000..e512585a60
--- /dev/null
+++ b/lib/rouge/demos/gnuasm
@@ -0,0 +1,39 @@
+        .global main
+        .type main, @function
+        .extern printf
+
+        .text
+/* Reads an integer,
+   doubles it,
+   and prints it. */
+main:
+        pushq %rbp
+        movq %rsp, %rbp
+        subq $128, %rsp  # Reserve 128 bytes for stack
+
+        # Read an integer into -8(%rbp)
+        movq $scan_format, %rdi
+        leaq -8(%rbp), %rsi
+        call scanf
+        # If invalid, jump to end
+        cmpq $1, %rax
+        jne .Lend
+
+        movq -8(%rbp), %rsi
+        imulq $2, %rsi  # Double the input
+
+        # Call 'printf("%ld\n", %rsi)'
+        movq $print_format, %rdi
+        call printf
+
+.Lend:
+        # Return with status 0
+        movq $0, %rax
+        movq %rbp, %rsp
+        popq %rbp
+        ret
+
+scan_format:
+        .asciz "%ld"
+print_format:
+        .asciz "%ld\n"
diff --git a/lib/rouge/guessers/disambiguation.rb b/lib/rouge/guessers/disambiguation.rb
index 17b064ef23..956777c21a 100644
--- a/lib/rouge/guessers/disambiguation.rb
+++ b/lib/rouge/guessers/disambiguation.rb
@@ -146,6 +146,13 @@ def match?(filename)
         next Prolog if matches?(/\A\w+(\(\w+\,\s*\w+\))*\./)
         next OpenEdge
       end
+
+      disambiguate '*.s', '*.S' do
+        next GnuAsm if matches?(/\s*\.(global|extern|type|text)/)
+        next GnuAsm if matches?(/%(r|e)(ax|bx|cx|dx|si|di|bp|sp)/)
+
+        ArmAsm
+      end
     end
   end
 end
diff --git a/lib/rouge/lexers/armasm.rb b/lib/rouge/lexers/armasm.rb
index 51b4a3885f..90b569d60b 100644
--- a/lib/rouge/lexers/armasm.rb
+++ b/lib/rouge/lexers/armasm.rb
@@ -7,7 +7,8 @@ class ArmAsm < RegexLexer
       title "ArmAsm"
       desc "Arm assembly syntax"
       tag 'armasm'
-      filenames '*.s'
+      filenames '*.s', '*.S'
+      mimetypes 'text/x-asm'
 
       def self.preproc_keyword
         @preproc_keyword ||= %w(
diff --git a/lib/rouge/lexers/gnuasm.rb b/lib/rouge/lexers/gnuasm.rb
new file mode 100644
index 0000000000..dc9f13a50c
--- /dev/null
+++ b/lib/rouge/lexers/gnuasm.rb
@@ -0,0 +1,64 @@
+# -*- coding: utf-8 -*- #
+# frozen_string_literal: true
+
+# Derived from nasm.rb. Not perfect.
+module Rouge
+  module Lexers
+    class GnuAsm < RegexLexer
+      title "GnuAsm"
+      desc "GNU Assembler"
+
+      tag 'gnuasm'
+      filenames '*.s', '*.S'
+      mimetypes 'text/x-asm'
+
+      state :root do
+        mixin :whitespace
+
+        rule %r/[a-z$._?][\w$.?#@~]*:/i, Name::Label
+
+        rule %r/([a-z$._?][\w$.?#@~]*)(\s+)(equ)/i do
+          groups Name::Constant, Keyword::Declaration, Keyword::Declaration
+          push :instruction_args
+        end
+        rule %r/\.[a-z0-9]+/i, Keyword, :instruction_args
+        rule %r/(?:res|d)[bwdqt]|times/i, Keyword::Declaration, :instruction_args
+        rule %r/[a-z$._?][\w$.?#@~]*/i, Name::Function, :instruction_args
+
+        rule %r/[\r\n]+/, Text
+      end
+
+      state :instruction_args do
+        rule %r/"(\\\\"|[^"\n])*"|'(\\\\'|[^'\n])*'|`(\\\\`|[^`\n])*`/, Str
+        rule %r/(?:0x[\da-f]+|$0[\da-f]*|\d+[\da-f]*h)/i, Num::Hex
+        rule %r/[0-7]+q/i, Num::Oct
+        rule %r/[01]+b/i, Num::Bin
+        rule %r/\d+\.e?\d+/i, Num::Float
+        rule %r/\d+/, Num::Integer
+
+        rule %r/[@$][a-z$._][\w$.?#@~]*/i, Name::Constant
+
+        mixin :punctuation
+
+        rule %r/%[a-z0-9]+/i, Name::Builtin
+        rule %r/[a-z$._][\w$.?#@~]*/i, Name::Variable
+        rule %r/[\r\n]+/, Text, :pop!
+
+        mixin :whitespace
+      end
+
+      state :whitespace do
+        rule %r/\n/, Text
+        rule %r/[ \t]+/, Text
+        rule %r/#.*/, Comment::Single
+        rule %r/\/\*(.|\n)*?\*\/*/, Comment::Multiline
+      end
+
+      state :punctuation do
+        rule %r/[,():\[\]]+/, Punctuation
+        rule %r/[&|^<>+*\/~=-]+/, Operator
+        rule %r/\$+/, Keyword::Constant
+      end
+    end
+  end
+end
diff --git a/spec/lexers/armasm_spec.rb b/spec/lexers/armasm_spec.rb
index 684a5bf242..a9a6d4b343 100644
--- a/spec/lexers/armasm_spec.rb
+++ b/spec/lexers/armasm_spec.rb
@@ -7,8 +7,8 @@
   describe 'guessing' do
     include Support::Guessing
 
-    it 'guesses by filename' do
-      assert_guess :filename => 'foo.s'
+    it 'guesses by filename and source hint' do
+      assert_guess :filename => 'foo.s', :source => 'Func MOVW    r0, #RetVal'
     end
   end
 end
diff --git a/spec/lexers/gnuasm_spec.rb b/spec/lexers/gnuasm_spec.rb
new file mode 100644
index 0000000000..55d34079cd
--- /dev/null
+++ b/spec/lexers/gnuasm_spec.rb
@@ -0,0 +1,14 @@
+# -*- coding: utf-8 -*- #
+# frozen_string_literal: true
+
+describe Rouge::Lexers::GnuAsm do
+  let(:subject) { Rouge::Lexers::GnuAsm.new }
+
+  describe 'guessing' do
+    include Support::Guessing
+
+    it 'guesses by filename and source hint' do
+      assert_guess :filename => 'foo.s', :source => 'main: movq %rax, %rbx'
+    end
+  end
+end
diff --git a/spec/visual/samples/gnuasm b/spec/visual/samples/gnuasm
new file mode 100644
index 0000000000..e512585a60
--- /dev/null
+++ b/spec/visual/samples/gnuasm
@@ -0,0 +1,39 @@
+        .global main
+        .type main, @function
+        .extern printf
+
+        .text
+/* Reads an integer,
+   doubles it,
+   and prints it. */
+main:
+        pushq %rbp
+        movq %rsp, %rbp
+        subq $128, %rsp  # Reserve 128 bytes for stack
+
+        # Read an integer into -8(%rbp)
+        movq $scan_format, %rdi
+        leaq -8(%rbp), %rsi
+        call scanf
+        # If invalid, jump to end
+        cmpq $1, %rax
+        jne .Lend
+
+        movq -8(%rbp), %rsi
+        imulq $2, %rsi  # Double the input
+
+        # Call 'printf("%ld\n", %rsi)'
+        movq $print_format, %rdi
+        call printf
+
+.Lend:
+        # Return with status 0
+        movq $0, %rax
+        movq %rbp, %rsp
+        popq %rbp
+        ret
+
+scan_format:
+        .asciz "%ld"
+print_format:
+        .asciz "%ld\n"