diff --git a/boilerplate/cairo-boilerplate-getopt.c b/boilerplate/cairo-boilerplate-getopt.c
index 6591598ae..be66ac235 100644
--- a/boilerplate/cairo-boilerplate-getopt.c
+++ b/boilerplate/cairo-boilerplate-getopt.c
@@ -94,7 +94,7 @@ static int permute_argv_once()
 }
 
 
-int _cairo_getopt(int argc, char** argv, char* optstr)
+int _cairo_getopt(int argc, char** argv, const char* optstr)
 {
 	int c = 0;
 
diff --git a/boilerplate/cairo-boilerplate-getopt.h b/boilerplate/cairo-boilerplate-getopt.h
index 6ed780c97..74bce14c7 100644
--- a/boilerplate/cairo-boilerplate-getopt.h
+++ b/boilerplate/cairo-boilerplate-getopt.h
@@ -48,7 +48,7 @@ extern int optind;
 extern int opterr;
 extern int optopt;
 
-int _cairo_getopt(int argc, char** argv, char* optstr);
+int _cairo_getopt(int argc, char** argv, const char* optstr);
 
 
 #ifdef __cplusplus