diff --git a/lib/lrama/lexer.rb b/lib/lrama/lexer.rb
index bd6e79bf..0073916f 100644
--- a/lib/lrama/lexer.rb
+++ b/lib/lrama/lexer.rb
@@ -157,6 +157,28 @@ def lex_c_code
 
       until @scanner.eos? do
         case
+        when @scanner.check(/\/\*/)
+          start_line = @line
+          start_column = column
+
+          @scanner.scan(/\/\*/)
+          comment_start = @scanner.matched
+
+          comment_location = Location.new(
+            grammar_file: @grammar_file,
+            first_line: start_line, first_column: start_column,
+            last_line: @line, last_column: column
+          )
+
+          comment_body = @scanner.scan_until(/\*\//)
+
+          if comment_body
+            chunk = comment_start + comment_body
+            code += chunk
+            chunk.count("\n").times { newline }
+          else
+            raise ParseError, comment_location.generate_error_message('Missing ‘*/’ at end of file') # steep:ignore
+          end
         when @scanner.scan(/{/)
           code += @scanner.matched
           nested += 1
@@ -202,6 +224,7 @@ def lex_comment
           newline
         end
       end
+      raise "Unterminated comment."
     end
 
     # @rbs () -> void
diff --git a/spec/lrama/lexer_spec.rb b/spec/lrama/lexer_spec.rb
index 05173778..1bd8297f 100644
--- a/spec/lrama/lexer_spec.rb
+++ b/spec/lrama/lexer_spec.rb
@@ -414,6 +414,20 @@
     end
   end
 
+  context 'missing_comment_end.y' do
+    it do
+      grammar_file = Lrama::Lexer::GrammarFile.new("invalid.y", "/* missing")
+      lexer = Lrama::Lexer.new(grammar_file)
+      lexer.status = :c_declaration
+
+      expect { lexer.next_token }.to raise_error(ParseError, <<~ERROR)
+        invalid.y:1:0: Missing ‘*/’ at end of file
+        /* missing
+        ^^
+      ERROR
+    end
+  end
+
   it 'lex a line comment without newline' do
     grammar_file = Lrama::Lexer::GrammarFile.new("comment.y", "// foo")
     lexer = Lrama::Lexer.new(grammar_file)