--- a/inst/pamdemod.m
+++ b/inst/pamdemod.m
@@ -21,8 +21,8 @@
 ## Demodulates a pulse amplitude modulated signal @var{x} into an
 ## information sequence of integers in the range @code{[0 @dots{} M-1]}.
 ## @var{phi} controls the initial phase and @var{type} controls the
-## constellation mapping. If @var{type} is set to 'Bin' will result in
-## binary encoding, in contrast, if set to 'Gray' will give Gray encoding.
+## constellation mapping. If @var{type} is set to "Bin" will result in
+## binary encoding, in contrast, if set to "Gray" will give Gray encoding.
 ## An example of Gray-encoded 8-PAM is
 ##
 ## @example
@@ -66,5 +66,5 @@
 
 endfunction
 
-%!assert (pamdemod ([-7:2:7], 8, 0, 'Bin'), [0:7])
-%!assert (pamdemod ([-7:2:7], 8, 0, 'Gray'), [0 1 3 2 6 7 5 4])
+%!assert (pamdemod ([-7:2:7], 8, 0, "Bin"), [0:7])
+%!assert (pamdemod ([-7:2:7], 8, 0, "Gray"), [0 1 3 2 6 7 5 4])