--- a/src/utils.h
+++ b/src/utils.h
@@ -32,30 +32,30 @@
 class octave_value_list;
 class string_vector;
 
-extern string search_path_for_file (const string&, const string&);
-extern string file_in_path (const string&, const string&);
-extern string fcn_file_in_path (const string&);
-extern string oct_file_in_path (const string&);
+extern std::string search_path_for_file (const std::string&, const std::string&);
+extern std::string file_in_path (const std::string&, const std::string&);
+extern std::string fcn_file_in_path (const std::string&);
+extern std::string oct_file_in_path (const std::string&);
 
 extern void jump_to_top_level (void) GCC_ATTR_NORETURN;
 
-extern int almost_match (const string& std, const string& s,
+extern int almost_match (const std::string& std, const std::string& s,
 			 int min_match_len = 1, int case_sens = 1);
 
 extern int
 keyword_almost_match (const char * const *std, int *min_len,
-		      const string& s, int min_toks_to_match,
+		      const std::string& s, int min_toks_to_match,
 		      int max_toks);
 
 extern int empty_arg (const char *name, int nr, int nc);
 
 extern const char *undo_string_escape (char c);
 
-extern string do_string_escapes (const string& s);
+extern std::string do_string_escapes (const std::string& s);
 
-extern string undo_string_escapes (const string& s);
+extern std::string undo_string_escapes (const std::string& s);
 
-extern int check_preference (const string& var);
+extern int check_preference (const std::string& var);
 
 extern void
 get_dimensions (const octave_value& a, const octave_value& b,