--- a/gtools.h	2021-09-03 04:19:20.000000000 -0600
+++ b/gtools.h	2022-07-01 10:22:31.451579384 -0600
@@ -287,7 +287,7 @@ extern void arg_sequence(char**,char*,lo
 extern void arg_sequence_min(char**,char*,long*,int,int,int*,char*);
 
 extern void writerange(FILE*,int,long,long);
-extern void gt_abort(const char*);
+extern void gt_abort(const char*) __attribute__((noreturn));
 extern char *stringcopy(char*);
 extern boolean strhaschar(char*,int);
 
--- a/nauty.h	2021-09-03 04:19:53.000000000 -0600
+++ b/nauty.h	2022-07-01 10:21:58.819514878 -0600
@@ -1353,7 +1353,7 @@ int leftbit[] =   {8,7,6,6,5,5,5,5,4,4,4
 extern "C" {
 #endif
 
-extern void alloc_error(const char*);
+extern void alloc_error(const char*) __attribute__((noreturn));
 extern void breakout(int*,int*,int,int,int,set*,int);
 extern boolean cheapautom(int*,int,boolean,int);
 extern void doref(graph*,int*,int*,int,int*,int*,int*,set*,int*,
--- a/showg.c	2022-01-27 15:24:09.078428828 -0700
+++ b/showg.c	2022-07-01 10:22:53.852623673 -0600
@@ -216,7 +216,7 @@ static long ogf_linelen;
 
 /************************************************************************/
 
-static void
+static void __attribute__((noreturn))
 gt_abort(char *msg)     /* Write message and halt. */
 {
     if (msg) fprintf(stderr,"%s",msg);