--- igraph-0.7.1/src/f2c/arithchk.c.FMT	2017-12-03 23:52:12.358833829 +0200
+++ igraph-0.7.1/src/f2c/arithchk.c	2017-12-03 23:55:05.102006735 +0200
@@ -93,41 +93,41 @@
 	struct {
 		double d;
 		int L;
 		} x[2];
 
 	if (sizeof(x) > 2*(sizeof(double) + sizeof(int)))
 		dalign = 1;
 	u.L[0] = u.L[1] = 0;
 	u.d = 1e13;
 	if (u.L[0] == 1117925532 && u.L[1] == -448790528)
 		return &IEEE_MC68k;
 	if (u.L[1] == 1117925532 && u.L[0] == -448790528)
 		return &IEEE_8087;
 	if (u.L[0] == -2065213935 && u.L[1] == 10752)
 		return &VAX;
 	if (u.L[0] == 1267827943 && u.L[1] == 704643072)
 		return &IBM;
 	return 0;
 	}
 
-char *emptyfmt = "";	/* avoid possible warning message with printf("") */
+const char * const emptyfmt = "";	/* avoid possible warning message with printf("") */
 
  static Akind *
 ccheck(void)
 {
 	union {
 		double d;
 		long L;
 		} u;
 	long Cray1;
 
 	/* Cray1 = 4617762693716115456 -- without overflow on non-Crays */
 	Cray1 = printf(emptyfmt) < 0 ? 0 : 4617762;
 	if (printf(emptyfmt, Cray1) >= 0)
 		Cray1 = 1000000*Cray1 + 693716;
 	if (printf(emptyfmt, Cray1) >= 0)
 		Cray1 = 1000000*Cray1 + 115456;
 	u.d = 1e13;
 	if (u.L == Cray1)
 		return &CRAY;
 	return 0;